Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

In another bowl, whisk together the flour, baking powder, and salt.

Gradually add the dry ingredients to the wet ingredients, alternating with the milk, and mix until just combined.

Divide the batter evenly between the prepared cake pans and smooth the tops.

Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.

Allow the cakes to cool in the pans for 10 minutes, then turn out onto wire racks to cool completely.

In a mixing bowl, whip the chilled heavy cream until soft peaks form. Gradually add the powdered sugar and vanilla extract, and continue to whip until stiff peaks form.

Once the cakes are completely cool, place one layer on a serving plate. Spread a layer of whipped cream on top, followed by half of the sliced strawberries, blueberries, and raspberries.

Place the second cake layer on top and repeat the process with the remaining whipped cream and berries.

Decorate the top with additional berries in a patriotic pattern, if desired. Chill the cake for at least 30 minutes before serving.