Preheat your oven to 350°F (175°C). Grease and line a 9x13 inch baking pan with parchment paper to prevent sticking.

In a large mixing bowl, combine the sifted flour, granulated sugar, baking powder, and salt. Mix dry ingredients together until well combined.

Add the softened butter, milk, eggs, and vanilla extract to the dry ingredients. Using an electric mixer, beat on medium speed for about 2-3 minutes until the batter is smooth and well blended.

Pour the batter into the prepared baking pan and spread evenly. Bake in the preheated oven for 25-30 minutes or until a toothpick inserted in the center comes out clean.

Once baked, remove the cake from the oven and allow it to cool in the pan for 10 minutes. Then, transfer it to a cooling rack to cool completely.

In a large mixing bowl, beat the softened butter with an electric mixer until creamy and smooth.

Gradually add the sifted powdered sugar, alternating with the heavy cream, and mix until fluffy. Add the vanilla extract and mix until combined.

Divide the frosting into three bowls. Leave one bowl white, color one bowl red with food coloring, and color the last bowl blue.

Once the cake is completely cool, spread a layer of white frosting evenly over the top of the cake.

Using a spatula, create horizontal stripes with the red frosting, leaving space for the blue section. Use a piping bag or a ziplock bag with the corner cut off for more precision.

In the top left corner, spread the blue frosting to create the 'stars' section of the flag.

Decorate the blue frosting with fresh blueberries to represent stars and arrange sliced strawberries in the red stripes.

Finish with a dollop of whipped cream around the edges for an extra festive touch.