In a saucepan, I mixed 1/2 cup heavy cream with 1 cup of milk and a tsp. of vanilla. I put 2/3 cup of flour to the side. Then waited for the milk to come to a simmer while stirring. Then, slowly added the flour while whisking it in so there wasn't any lumps in my frosting. As soon as it turned thick, I put it in a bowl, covered it and popped it in the fridge.
In my mixer, I put 3 sticks of unsalted butter and added 3 cups of powdered sugar. I mixed it real well and then slowly added the cold paste a little at a time until all mixed.
PIPING TRICK: Plop a big heap of frosting on a rectangle of saran wrap. fold the wrap over the frosting both sides and then wind the ends. It should look like old fashioned hard candy wrapper. When ready to pipe, cut one end of the saran wrap and put it down into the piping bag. It makes it easy to use the piping bag multiple times while keeping the bag nearly clean.
I used a large round tip and sprinkled them with sugar sprinkles. **The frosting is best after setting up in the fridge for a bit...or as long as you can resist.