Homemade Blueberry Biscuits

Preheat the oven to 425°F and line a sheet pan with parchment paper.
In a large bowl, whisk together flour, sugar, baking powder, cream of tartar, and salt.
Add 8 tablespoons of cubed butter and use your fingers to toss the butter and coat each cube in flour. Press each cube between your thumb and forefinger to shape it into a flat disc.
Add the blueberries to the flour and butter and toss well with your fingers to mix everything together.
In a medium bowl, whisk together the egg, vanilla, sour cream, and milk until smooth.
Pour the wet mixture over the dry ingredients. Stir with a wooden spoon until the dough is starting to come together.
Using your hands, fold the dough over itself several times, pressing the dough together and rotating the bowl in between folds, until all of the flour is incorporated.
Divide the dough into eight equal portions, about 128 grams each. Transfer each one to the prepared baking sheet, pressing it lightly into a rounded mound.
Melt the remaining two tablespoons of butter and brush over the tops of the biscuits.
Bake for 16-18 minutes, until the tops are lightly browned and the bottoms of the biscuits are golden.
Serve immediately with jam, butter, cream cheese, or lemon curd. Cool completely before storing any leftovers in an airtight container.