Preheat the oven to 350°F (175°C). Grease two 8-inch round cake pans and line the bottoms with parchment paper.

In a medium bowl, whisk together the flour, baking powder, and salt until evenly combined.

In a large bowl, beat the softened butter and granulated sugar until light and fluffy. Add the eggs one at a time, beating well after each addition, then stir in the vanilla extract.

Gradually add the dry ingredients to the butter-egg mixture in three additions, alternating with the milk. Mix only until just combined.

Divide the batter evenly between the prepared pans and smooth the tops. Bake for 22–25 minutes or until a toothpick inserted in the center comes out clean.

Cool the layers completely on a wire rack.

Combine the blueberries, 1/4 cup sugar, and lemon juice in a saucepan over medium heat. Stir in the cornstarch slurry until thickened, then cool to room temperature.

Whip the heavy cream with powdered sugar and vanilla until stiff peaks form. Keep chilled until assembly.

Place one cake layer on a serving plate. Spread an even layer of blueberry filling, then a generous layer of whipped cream. Top with the second cake layer and cover with remaining whipped cream.

Chill for at least 2 hours to set before serving.