Place a small amount of sprinkles in a small bowl.
Spray the blades of a clean scissors with cooking spray or wipe lightly with a paper towel that's been dipped in oil. Wipe off any excess oil. (If blades of the scissors begin to get sticky at any point, just wash the scissors with hot water, dry well and repeat oil.
Cut about 16-18 marshmallows in half, diagonally and add them to the bowl with sugar. Stir to coat sticky, cut side of marshmallow halves with colored sugar.
Cut 1 marshmallow in half crosswise and place sticky side down into sprinkles (or nonpareils). Push down on marshmallow half to enlarge it to a circular "button". Remove from sprinkle bowl and set aside. Repeat with the other half.
Beginning at the outer edge of the frosted cupcake, place marshmallows all the way around the cupcake. When you apply them, pinch the end facing outwards for the "poinsettia look". When the outer circle is complete, move in and do the same thing again. The last circle of petals should be right around the "button". (I use 14-16 "petals" around the outer edges. 10-12 around the middle circle and 6-7 around that surrounds "the button.)
With your hands slightly cupped, gently shape the flower so that it's circular and some outer petals aren't sticking out.
Repeat procedure for remaining cupcakes.
See Café Tips in the post above for detailed instructions and tips to ensure success.
The video in the post above demonstrates all these steps.