Line the bottom of any glass or porcelain baking dishes with parchment paper. Then, oil any type of baking pan or dish with nonstick gluten free spray oil. If using paper, oil the top of the paper as well as the sides.
In the bowl of your electric mixer, combine all of the dry ingredients (flour blend, baking powder, baking soda, salt, and sugars).
Add the buttermilk, oil, and vanilla; beat on medium speed for about 2 minutes.
Using a silicone/rubber spatula, fold in the sprinkles, if using.
Divide the batter evenly among the pans, if making more than one layer.
Run a butter knife through the batter back and forth to remove any large pockets of air. (This is important for thick batters.)
Microwave each layer individually for 1 - 5 minutes, depending upon the size pan, its material, and the wattage of your microwave. (Using a 9 x 9 glass casserole dish may take as long as 5 minutes where a 4-inch creme brulee ramekin only takes 55 seconds in a 1200 watt microwave.) Try not to overcook the cake as this creates a rubbery texture.
Allow the cake(to rest in the baking container for 5 minutes or until you can comfortably handle it/them. Remove the cake from the pan and remove and discard the parchment paper. Transfer to a wire rack to cool completely. If you wish to slice off the dome of cake, for staking for a layer cake, refrigerate for at least 15 minutes. Then, slice off the dome.