Preheat oven to 350°F. Grease and line three 9-inch cake pans.
Mix flour, baking powder, and salt.
Cream butter and sugar until fluffy (5 minutes). Add eggs one at a time, then vanilla.
Alternate adding dry ingredients and milk to butter mixture.
Divide batter between pans. Bake 25-30 minutes.
Cool completely.
Whip cream to soft peaks. Mix mascarpone, powdered sugar, vanilla, and salt separately. Fold together.
Macerate berries with sugar and lemon juice for 15 minutes.
Layer cake: cake, cream, berries. Repeat.
Frost exterior with remaining cream.
Garnish with fresh berries and mint.