Ingredients

For the cake:
• 2 cups (250g) all-purpose flour
• 1½ tsp baking powder
• ½ tsp baking soda
• ½ tsp salt
• ¾ cup (1½ sticks / 170g) unsalted butter, softened
• ¾ cup (150g) granulated sugar
• 2 large eggs
• 1 tsp vanilla extract
• ¾ cup (180ml) sour cream or full-fat Greek yogurt
• 1½ cups fresh or frozen blueberries (if frozen, do not thaw)

For the streusel topping:
• ¼ cup (50g) granulated sugar
• ¼ cup (55g) packed brown sugar
• 1 tsp ground cinnamon
• 3 tbsp all-purpose flour
• 3 tbsp cold unsalted butter, cubed

Instructions

Preheat oven to 350°F (175°C). Grease a 9″ round or square baking pan; line bottom with parchment.
Streusel: In a small bowl, mix sugars, cinnamon, and flour. Cut in cold butter with fingers or fork until crumbly. Set aside.
Cake: Whisk flour, baking powder, baking soda, and salt in a bowl.
In another bowl, beat butter and sugar until light (~3 min). Add eggs one at a time, then vanilla.
Alternate adding dry ingredients and sour cream to wet mixture, beginning and ending with flour. Gently fold in blueberries.
Spread batter into pan. Sprinkle streusel evenly over top.
Bake 40–45 minutes until golden and a toothpick comes out clean (tent with foil if topping browns too quickly).
Cool 15 min before slicing. Best served warm or at room temperature!