Preheat oven to 325° F. Coat an 8-inch square cake pan with cooking spray and parchment paper, if desired.
In a medium bowl, add flour, baking powder, baking soda, and salt. Stir with a whisk to combine. Set aside.
2 cups cake flour, ½ teaspoon baking powder, ½ teaspoon baking soda, ⅛ teaspoon salt
In a separate medium sized bowl, add the sugar, butter, vanilla, and the zest of one lemon. Beat with a mixer at high speed until well blended.
¾ cup sugar, ¼ cup unsalted butter, softened, 2 teaspoons vanilla extract, Zest of two lemons
Add the flour mixture to the sugar mixture a little at a time alternating with the buttermilk, starting and ending with the flour mixture. Mix just until almost combined.
1 cup buttermilk
Toss 1 cup of blueberries with 1 tablespoon of flour until they are fully coated. Add the blueberries to the batter.
3 cups blueberries
Using a rubber spatula, fold the blueberries into the batter just until combined.
Pour the batter into the prepared 8-inch square cake pan. Use an offset spatula to spread the batter to the edges and corners.
Bake in the 325° F oven for 40-43 minutes or until cake begins to pull away from the sides of the pan. Transfer pan to a cooling rack to cool. Cut into 16 squares.
While the cake is cooling, prepare the compote. Place 1 ⅓ cups of blueberries into a medium microwave safe bowl.
Microwave on high for 3-4 minutes or until bubbly. Add the lemon zest and stir to combine. Serve warm drizzled over individual cake slices.