In a small bowl, mix together the peanut butter and powdered sugar until combined. On a piece of wax paper, roll peanut butter mixture into 24 half-teaspoon balls and set aside.*
In another small bowl, microwave the mini marshmallows for 30 seconds. Remove from microwave and stir in corn syrup. On another piece of wax paper, roll fluff mixture into 24 half-teaspoon balls and set aside.*
Set out 24 mini cupcake molds on a large baking sheet. Melt 1.5 cups of your white chocolate in a double boiler, being very careful not to overheat the chocolate or it will seize. Spoon a little less than 1 teaspoon of white chocolate into the bottoms of each mini mold. Bang the baking sheet several times on a hard surface to even out the chocolate. Place in freezer for 5 minutes to harden.
Place a peanut butter ball in the center of your mold, flattening slightly but not so much that it reaches the edge of the mold. Using your fingers, flatten the fluff ball into a small pancake the size of a dime. Place on top of peanut butter. Place in freezer for 5 minutes to harden.
Melt the rest of your white chocolate in the double boiler. Scoop 1.5-2 teaspoons of white chocolate over the molds and again bang the baking sheet several times on a hard surface to even out the chocolate. Allow to cool in the freezer for 5-10 minutes, then serve!
*It helps to have a small bowl of water at your side. Dip your fingers into the water before rolling out your balls. This will help to prevent sticking and will help to hold the balls together.