Preheat the oven to 350°F (175°C). Grease and flour two 8-inch round cake pans.

In a mixing bowl, combine flour, sugar, baking powder, baking soda, and salt.

Add softened butter, eggs, vanilla extract, and milk. Beat with an electric mixer on medium speed for 2-3 minutes until smooth.

Divide the batter evenly between the prepared cake pans.

Bake for 25 minutes or until a toothpick inserted in the center comes out clean. Let cool in pans for 10 minutes, then transfer to wire racks to cool completely.

In a mixing bowl, beat softened butter until creamy.

Gradually add powdered sugar, alternating with heavy cream and vanilla extract. Beat until fluffy.

Divide frosting into two bowls and tint one with blue food coloring and the other with pink.

Place one cake layer on a serving plate. Spread a layer of blue frosting on top.

Add the second cake layer and frost the top and sides with pink frosting.

Roll out fondant and cut into fish shapes. Decorate the cake with fondant fish and sprinkle with edible glitter if desired.