1cup + 2 Tablespoonslight brown sugarfirmly packed (225g)
10Tablespoonsunsalted buttermelted and cooled until no longer hot to the touch (140g)
Preheat oven to 350F (175C) and lightly grease and flour a 13x9 baking pan.⁴
Combine butter, cream cheese, and sugars and use an electric mixer (or a stand mixer) to cream together ingredients until well-combined, light, and fluffy.
Add eggs and vanilla extract and beat on medium-low speed until combined, pausing to scrape the sides and bottom of the bowl.
In separate bowl whisk together flour, baking powder, cornstarch and salt.
Add about 1/4 of the flour mixture and stir on low speed until just combined. Add about 1/3 of the buttermilk and stir until combined. Continue to alternate adding flour and buttermilk until all are added and mixture is completely combined.
Use a spoon or spatula to stir in the blueberries.
Spread batter into prepared pan (batter will be thick) and prepare streusel, if using.
To make streusel, whisk together flour, sugars, and salt. Drizzle in melted butter and use a fork to stir/toss together until mixture is clumpy but combined (all the butter should be absorbed). Do not use butter that is too hot and do not over-mix or the mixture will be like a paste! It should be clumpy and crumbly.
Sprinkle streusel evenly over batter.
Bake on 350F for 55-60 minutes or until a toothpick inserted in the center yields moist crumbs or no crumbs.
Allow to cool before cutting and serving.
¹Buttermilk: You may substitute regular milk, but the cake may not be quite as flavorful or moist. You can also try my buttermilk substitute.²Blueberries. You can use fresh or frozen blueberries. Do not thaw if using frozen.³Streusel. You may omit the streusel completely or substitute a simple sprinkling of granulated sugar instead. The blueberry coffee cake will need less time in the oven (start checking at 40 minutes).⁴Baking pan. I bake this recipe in a metal baking pan. If using a glass baking dish you will most likely need more time in the oven.