In a large bowl, beat all ingredients together until smooth and fluffy. Start with 3 cups of powdered sugar and gradually add more until the right consistence is obtained. If you add too much, balance it out with more milk, 1 Tbsp at a time.
Cut the tops off each layer so that they are flat. Place the first layer on a serving dish, then "plop" a generous scoop of icing on top. Spread out from the middle until you have a solid layer.
Gently put the second layer on top, and repeat the icing process.
Repeat with a final layer, and spread icing on top to form a smooth layer.
To ice your sides, spread small spoonfuls all over the sides of the cake, and with a long icing spreader or paddle, scrape the sides all the way around so that you have a "bare" iced look. This step doesn't have to be perfect, so make it look however you like.
Top with sprinkles or decorations of your choice. Cut and serve.
Notes: Cake can be made into three thick layers or four smaller layers - great to customize.
Want flavoring? Add some strawberry flavoring oil or other flavors to the icing when mixing.
Customize this cake by adding as much or as little decorations as you like, including edge icing, different sprinkles, mini chocolate chips, or fresh fruit such as berries on top.