Blueberry Coffee Cake with Oat Crumble Topping

In the peak of summer, highlight fresh blueberries with this Blueberry Coffee Cake with Oat Crumble Topping! A moist and tender yellow cake is studded with juicy blueberries, featuring their naturally vivid purple color and sweetness. The oat crumble topping is buttery and crisp and a perfect contrast in texture, with brown sugar and subtle cinnamon aroma. This one disappears from the kitchen counter almost as quickly as I can make it!

We are lucky to be able to pick fresh, local blueberries during the summer months and I'm always looking for ways to feature their delicious flavor. This blueberry coffee cake puts them on display! You can also make this recipe with frozen blueberries, so no need to miss out any time of year.

Enjoy your blueberry coffee cake for dessert, as an afternoon snack, or at breakfast! Just like this Cardamom Coffee Cake, Chocolate Chip Coffee Cake, or Sweet Focaccia with Blueberries, it's perfect any time of day.

Ingredients for Blueberry Coffee Cake

I include ingredient notes here when I think they'll be helpful, including ways to source, any preparation tips, or why I've chosen a particular ingredient. Be sure to check out the recipe card below for the full list of ingredients and their quantities!

• Vegetable Oil - Use vegetable oil, corn oil, avocado oil, canola oil, or another neutrally flavored oil to get a tender cake layer that won't dry out.
• Eggs - Two large eggs help build the tender and moist structure of the cake.
• Greek Yogurt - Use 2% or whole milk Greek yogurt to add richness to the cake batter as well as a lightly tangy flavor. The acidity in the yogurt also contributes to the leavening and rise of the cake.
• Granulated Sugar - Plain white sugar will provide sweetness and contribute to a tender, light crumb in the coffee cake.
• All-Purpose Flour - All-purpose flour has a moderate protein content that will deliver a tender cake with enough heft to support the blueberries. Measure your flour by scooping and leveling it into a measuring cup to avoid packing it in. Or, use a kitchen scale for the most accurate baking.
• Baking Powder - Baking powder is the leavening agent in the coffee cake and provides both the acid and the base component that, when activated with moisture, produces air bubbles and creates lift. 
• Blueberries - Use fresh blueberries in the height of summer or frozen blueberries all year round in this recipe. If you are using frozen blueberries, do not thaw them for this recipe. Simply add them to the dry ingredients directly from the freezer. Baking time will be a bit longer with frozen berries than with fresh berries.

Ingredients for Oat Crumble Topping

• Salted Butter - Use room temperature salted butter so that you can easily blend the oats, sugar, and flour into an even mixture. If you only have unsalted butter on hand, add ¼ teaspoon of salt to your crumble mixture.
• Brown Sugar - Brown sugar adds a subtle molasses flavor and extra moisture to the oat crumble. Make sure you pack your brown sugar into the measuring cup firmly, or use a kitchen scale to measure it out.
• All-Purpose Flour - Flour helps the oat crumble bake up into a crisp topping with light texture.
• Rolled Oats - Use rolled oats or old-fashioned oats for this recipe. Oats add a toothsome texture to the topping for textural contrast to the tender cake.
• Cinnamon - Just a bit of ground cinnamon adds a classic aroma and subtle spice to the topping that doesn't overwhelm the blueberry flavor.
• Baking Powder - Adding baking powder to the crumble topping helps it puff up just a bit for a lighter topping texture.

Instructions

Preheat your oven to 350°F and spray a 9-inch round pan with baking or cooking spray.

In a large bowl, add the oil, eggs, yogurt, milk, granulated sugar, and vanilla.

Whisk the wet ingredients until they are completely smooth.

In a medium bowl, add the flour, baking powder, and salt. Mix the dry ingredients with a fork.

Add the blueberries to the dry ingredients and toss them well so that they are evenly coated with flour.

Add the flour mixture directly to the wet ingredients in the large bowl.

Top Tip

For clean slices and easier serving, allow the cake to cool at least an hour (or completely) before slicing. Use a serrated knife, like a bread knife, to slice through the crumble topping and tender cake.

Substitutions and Variations

The substitutions listed below have been tested in this recipe and work well. If you successfully make any other ingredient substitutions, let us know in the comments!

• Sour Cream Coffee Cake - Swap sour cream for the Greek yogurt to get a sour cream coffee cake that has tender crumb and a little bit of tang.
• Use Vanilla Bean Paste - To get a deeper vanilla flavor in the yellow coffee cake base, use a vanilla bean paste. You can use the same amount of paste as extract and your cake will have visible specks of vanilla!
• Add Spices - Add additional ground spices to the oat crumble like ½ teaspoon of ginger or ¼ teaspoon of nutmeg. This will make an extra fragrant topping with subtle spice flavor.

Equipment

You'll need a sturdy baking pan for this recipe, but here are some other notes on the equipment I used to make this delicious coffee cake turn out perfectly:

• 9-Inch Round Cake Pan - A round cake pan is a classic for layered birthday cakes, but it also makes for a nice presentation for quick breads and coffee cakes like this blueberry coffee cake. When you need to substitute a different sized pan, keep the surface area of the bottom of the pan as well as the depth in mind. A 9-inch round cake pan has a surface area of about 64 inches squared, similar to an 8-inch square pan, so these are generally interchangeable.
• Serrated Knife - A serrated knife, or bread knife, is usually a long blade with "teeth" on the cutting edge. These are great for cutting through crusty loaves of bread, textured toppings on baked goods, fillo dough crusts, and more. You can also use a serrated knife as a tomato knife in a pinch! In this recipe, a serrated knife slices through the oat crumble topping but won't compress the texture of the coffee cake. 
• Mixing Bowl - It's helpful to have mixing bowls in a variety of sizes, but you'll always reach for a sturdy glass or stainless steel mixing bowl for mixing batters, cookie doughs, snack mixes, and salads. Bigger is better, usually! It's the worst to try to mix carefully in a too-small bowl.

Serving Suggestions

Serve your pretty blueberry coffee cake at brunch with a fruit salad, bacon, and fresh coffee. It also makes a delicious mid-afternoon or after-school snack! Serve it with a scoop of vanilla ice cream and a drizzle of blueberry simple syrup for a summer dessert.

Storage

Blueberry coffee cake can be stored at room temperature for up to two days. Either tightly cover the baking pan with foil or transfer the slices to an airtight container. You can also store slices in an airtight container in the refrigerator for up to 5 days, but we've never had the coffee cake last that long!

Make Ahead Options

Because the coffee cake can be stored at room temperature for a couple of days, feel free to make it a day ahead of time for breakfast or brunch. The oat crumble topping is crisp on the first day, but softens a bit the second day.