Preheat your oven to 350 degrees Fahrenheit and generously grease a 13x18 inch baking pan and set aside.
In a large bowl, beat the butter and sugar until fluffy.
Next, add the vanilla and eggs and mix together until smooth.
In a separate medium bowl add the flour, baking powder, and salt and whisk together.
Add the dry ingredients into the wet ingredients along with the milk and mix until combined.
Pour the batter into your prepared baking sheet and bake in your oven for 18-20 minutes until a toothpick comes out clean. Remove the cake from the oven and allow it to cool completely.
While the cake is cooling, make the frosting. Add all the frosting ingredients in a bowl and beat until fluffy. Add additional heavy cream or powdered sugar to reach your desired consistency.
Once the cake has completely cooled, use a 3-inch circle cutter to cut the cake into little rounds. You should be able to cut out 12-15 individual circles.
Next create your mini cakes, take a circle of cake and top with some frosting, repeat until you have 3 layers of cake.
Once you have your layers and frosting between each layer, coat the outside of the cake with frosting. Then transfer some of the frosting to a piping bag and pipe decorative stars around the top and bottom edges of the cake and sprinkle with rainbow jimmies.
Finally, serve and enjoy!
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Notes
You can store leftovers of these mini cakes in an airtight container at room temperature for 1-2 days. For longer storage place in your fridge for up to 5 days.You can freeze these cakes and store them in your freezer for up to 2 months.