Preheat oven to 350F degrees. Line muffin tin with 12 cupcake liners. Set aside.
In a medium bowl, mix together flour, baking powder, baking soda, and salt. Set aside. In a large microwave-safe bowl, melt butter in the microwave. Whisk in sugar – mixture will be gritty. Chill in the refrigerator for 1 minute. Stir in egg, yogurt, milk, and vanilla extract until combined. Slowly mix in dry ingredients until no lumps remain. Batter will be thick. Slowly stir in sprinkles, but do not overmix because the sprinkles will bleed their color.
Divide batter among 12 cupcake liners (or 24 mini) and bake for up to 20 minutes or until a toothpick inserted in the center comes out clean. Bake for 8-9 minutes if making mini cupcakes. Allow to cool.
Sift 3 cups powdered sugar & cocoa powder into a medium bowl. Set aside.
On medium speed, cream butter for a few minutes in a stand mixer with the paddle attachment. Turn speed to LOW and slowly pour in the dry ingredients. Be careful so that the dry ingredients do not blow everywhere! Mix until sugar/cocoa are absorbed by the butter.
Turn up mixer to medium speed and add the vanilla and salt. Slowly add in the half + half (or milk or cream) and beat for about 2 minutes or until the frosting reaches a desired thickness. Add the last 1/2 cup of powdered sugar if needed to increase frosting thickness. Fold in the chopped candies.
Pipe or spread the frosting onto the cooled cupcakes. Decorate with additional sprinkles, if desired. For the finishing touch, add a single pretzel egg to each cupcake.