Preheat oven to 350°F (175°C). Grease and flour two cake pans.

Cream together butter and sugar until light and fluffy. Add eggs one at a time, mixing well.

Gradually add flour, baking powder, and salt, alternating with buttermilk and vanilla extract. Mix until just combined.

Pour batter into prepared pans and bake for 25-30 minutes or until a toothpick comes out clean. Cool in pans for 10-15 minutes, then transfer to a wire rack.

Combine blueberries, sugar, and lemon juice in a saucepan. Simmer over low heat, stirring occasionally, until blueberries soften and release juices, creating a thick sauce.

Chill a bowl and beaters in the freezer for 15 minutes. Whip cold heavy cream on medium speed until soft peaks form.

Add sugar and vanilla, continue whipping until stiff peaks form.

Trim cake layers if needed. Place one layer on a stand, spread with blueberry filling and whipped cream. Top with second layer and frost with remaining whipped cream.