Combine butter and marshmallows in a large bowl and microwave on high for 1 minute 30 seconds. Stir a few times and add in Rice Krispie cereal. Stir well to combine. Press into a greased 9x13 pan. Cool completely. (I was impatient so I stuck mine in the freezer for 10 minutes!)
Turn cooled treats onto a cutting board. Using different sizes of biscuit cutters, cut circles, then use a much smaller cutter to cut the donut holes out of the middle. Depending on what size of circles you cut, you will likely get 10-12 donuts. I use my Ateco Cutters- they're perfect for this since they come in a variety of sizes.
Melt each of the chocolates in small bowls. Dip Krispie Donuts into chocolate, filling in with a spoon where needed. Drizzle on additional chocolate if you'd like. Sprinkle colored jimmies on top. Let cool completely until set.