Preheat the oven to 350?F (175?C). In a mixing bowl, cream together the softened butter, granulated sugar, and brown 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, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Fold in the mixed berries gently.

Pour the batter into a greased baking sheet and spread evenly. Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.

Remove from the oven and let cool on a cooling rack.

In a bowl, mix the powdered sugar, milk, and softened butter until smooth. Divide the frosting into two bowls and color one red and the other blue with food coloring.

Once the cake is completely cooled, spread the white frosting on top. Use the red and blue frosting to create festive designs.

Slice and serve at your Fourth of July party!