Cook popcorn in microwave according to package directions.

In medium saucepan heat marshmallows,2 tablespoons butter and peanut butter until it's smooth and creamy.

Place popcorn in a large bowl.

Pour marshmallow mixture over popcorn and stir until it's coated all the popcorn.

Stir in peanut butter candies.

In a baking pan (I used a 7-inch pan with a with removable bottom) butter the bottom and sides with remaining 1 tablespoon of butter (you may only need 1/2 tablespoon butter) be sure the pan is coated completely

Place pan in the refrigerator so it chills and the popcorn mixture is set about an hour.

Remove popcorn cake from pan,

place the cake on a tray with a slotted cooling rack so the chocolate that is poured over will drip and not pool at the bottom of the cake.

Melt the chocolate completely.

Pour chocolate over popcorn cake.

Use an offset spatula to spread the chocolate over the top evenly and down the sides until the whole cake is covered.

Top with sprinkles.

Place cake in the refrigerator to set chocolate about 10 minutes.

Remove from the refrigerator.

The cake can remain at room temperature until served.