LEMON BLUEBERRY LAVENDER CAKE WITH MASCARPONE BUTTERCREAM FROSTING

LEMON BLUEBERRY LAVENDER CAKE WITH MASCARPONE BUTTERCREAM FROSTING
Made this cake and it was delicious! The only thing is, and this may be a rookie mistake, the icing curdled. I assume from over mixing the mascarpone icing. Is there anyway to prevent this? Should I mix the butter and powder sugar first and then fold in the mascarpone??
INGREDIENTS
FOR THE CAKE

• 1/3 cup lemon juice
• 3 3/4 cups all purpose flour
• 1 teaspoon baking powder
• 1 teaspoon sea salt
• 3 large eggs, room temperature
• 2 egg whites, room temperature
• 2 cups granulated sugar
• 1 teaspoon baking soda
• 1 teaspoon lavender extract
• 1 1/2 cups unsalted butter, room temperature
• 1 1/2 cups buttermilk
• 1 1/2 cups fresh blueberries, plus extra for garnish
• Lemon slices, culinary lavender buds for garnish
• 1 tablespoon lemon zest
• 2 teaspoons vanilla extract

FOR THE JAM

• 6 ounces blueberries
• 1 teaspoon lemon zest
• 1 tablespoon lemon juice
• 2 tablespoons water
• 1/4 cup granulated sugar

FOR THE FROSTING

• 1 1/2 cups unsalted butter
• 1 teaspoon lemon zest
• 1 teaspoon lavender extract
• 1 teaspoon vanilla paste (if unavailable, you can substitute vanilla extract)
• 3 cups powdered sugar
• 2 tablespoons heavy cream
• 8 ounces mascarpone

Source : aberdeenskitchen.com