• Preheat oven to 350℉/180℃. Line your 9x9 baking pan with parchment paper and set aside.

For the streusel

• In a medium-sized bowl, add cold butter, sugar, and flour. Mix until a crumb forms. This will be your streusel. Set aside in the fridge to chill as you make the cake batter.
  3/4 cups all-purpose flour, 1/3 cup white sugar, 6 tbsp butter

For the cake

• In a large bowl, add in the flour, white sugar, baking powder, and salt. Mix together.
  3/4 cups white sugar, 1 3/4 cups all purpose flour, 1 3/4 tsps baking powder, 1/4 tsp salt
• In the same bowl as the dry ingredients, add in about 1/3 of the butter. Mix on low, and keep adding in the butter until a crumbly texture forms. The key to a tender cake is mixing as little as possible, so only mix until just combined!
  3/4 cup unsalted butter
• Add the eggs in one at a time, mixing in between each addition. Then, add in the vanilla. On low speed, continue mixing until just combined.
  1 tbsp vanilla extract, 3 eggs
• Mix in the milk, making sure it's well incorporated. The batter will be smooth. If it is clumpy, this means your wet ingredients weren't at room temperature before beginning.
  1/3 cup milk *
• Gently toss the blueberries in 1 tbsp of flour and evenly coat them. Then add them into the batter and mix until just combined. Tossing them in the flour helps prevent them from sinking to the bottom while it bakes.
  2 cups fresh blueberries
• Add the batter into the prepared pan and spread evenly.
• Sprinkle the streusel on top and bake for 45-60 minutes. Every oven differs, so keep an eye on it after 40 minutes. Mine took 57 minutes exactly. The cake will be ready when a toothpick inserted comes out clean.