Step 1: In a stand mixer, combine all-purpose flour, granulated sugar, baking powder, and salt. Mix the dry ingredients well, then add softened unsalted butter until crumbly. Whisk buttermilk, eggs, almond extract, and vanilla extract together, gradually adding to dry ingredients, mixing on medium speed for about 2 minutes.

Step 2: Preheat your oven to 335°F (170°C). Grease three 8-inch cake pans. Divide the batter among the pans and smooth the tops. Bake for 30-35 minutes until golden brown and a toothpick comes out clean.

Step 3: Cool the cakes in pans for 10 minutes before transferring to wire racks to cool completely. Trim any crusty edges if necessary.

Step 4: In a bowl, beat mascarpone cheese, sugar, and vanilla extract until smooth. In another bowl, whip the heavy cream to firm peaks and gently fold it into the mascarpone mixture.

Step 5: In a saucepan, combine mixed berries, sugar, and a little water over medium heat, stirring until the sugar dissolves. Simmer for 5-7 minutes until thickened. Let it cool completely.

Step 6: Assemble the cake starting with one layer, brushing with berry syrup and spreading a layer of mascarpone frosting, followed by fresh berries. Repeat with remaining layers and frost the exterior of the cake.

Step 7: Decorate with extra mixed berries and chill for at least 30 minutes before serving.