Decide if you want one layer cakes or two layer cakes (the depth of your cup can help decide this).
Prepare cake according to recipe or package directions. For a single layer dot cake, bake in one 9x13-inch pan. For a double layer dot cake (as shown), bake in two 9x13-inch pans. Line your pan(s) with parchment paper for easy removal of the cakes after they cool.
Bake as directed; baking time will be cut approximately in ½ - ⅔ time for a single layer, so check after half the time called for on your recipe/box. Cool completely.
Use the cup or jar you're using for your dot cakes to cut rounds of cake. Nestle each cut as close together as possible (and you can use scraps to make additional cakes).
If making a single layer, place the cake in the jar. If making a double layer, place one layer in, add frosting, then add the second layer.
Top the cakes with frosting all the way to the top of the cup, flush with the edge.
Place sprinkles in a bowl. Holding the bowl over the sink, dip the dot cake upside down and press to coat with sprinkles. Repeat with rest of cakes. Chill until set.
Store in refrigerator, covered, for up to 3 days or freeze for up to a month.