Flour your work surface generously and rolling pin lightly. Divide the dough in half. Roll the first half as evenly as you can into a 1/4-inch square and add about a tablespoon of sprinkles to the top of the dough. Using your hands, press the sprinkles into the dough, fold it over and roll it out once more. Add another tablespoon of sprinkles and then fold it over again. Lastly, roll it out to a 1/4-inch thick square that’s about measures to be about 14 x 14 inches.
Using an offset spatula or clean hands, rub spread half of the butter onto the surface of the dough square, stoping 1/2-inch from the edges. Sprinkle and spread half of the filling sugar mixture until it’s one even layer. Starting from the opposite long side, roll the dough toward you, snuggly but not so tightly that you push the filling out. When rolled completely, pinch the seam together.
Lightly flour a cutting board and transfer the roll to it. Put the roll in the freezer to chill for about 10 to 15 minutes—this helps with slicing. Repeat that entire process with the second half of the dough.
With a sharp serrated knife, cut the roll crosswise into buns 1 1/2-inch thick, using a sawing motion to avoid pressing down on the roll. Transfer the buns to two lightly greased 9” cake pans and space them about 1-inch apart. (A variety of baking dishes can be used.) Repeat this entire process with the remaining dough and filling. Cover the buns with a clean kitchen towel and allow them to rise in a draft-free part of your house until they’re puffy and doubled in size, about 1 hour.