3cupsmilk or semi-sweet chocolate chipsor a combination of both (2 bags total)
1/2cupwhite chocolate chips
Line a jelly roll (or half sheet pan) with parchment paper.
Using a hand or standing mixer, beat together cooled melted butter, peanut butter, sugar, and vanilla until smooth and creamy. Add in the powdered sugar and beat until thoroughly combined.
Press the peanut butter mixture into the sheet pan - spreading it evenly to about a 1/2" thickness.
Place the sheet pan in the freezer for about 15 minutes.
Lift the chilled peanut butter mixture from the sheet pan and set onto a hard surface or cutting board.
Use a cookie cutter to cut out heart shapes from the peanut butter sheet.
Place the cut shapes onto a sheet of parchment paper and place them back into the freezer.
The remnant peanut butter mixture can be pressed back into a 1/2" flat sheet so that you can cut out additional shapes.
After the cutouts have chilled for 25 minutes, prepare the chocolate for dipping.
Place chocolate chips in a heatproof bowl with 2 tablespoons of shortening. Heat in 30-second increments, stirring between each blast, until the chocolate is mostly melted.
Stir chocolate until completely smooth and it drizzles easily.
Remove just one or two chilled peanut butter hearts from the freezer at a time. Use a fork to dip the heart into the melted chocolate and flip it to coat both sides. Lift from the chocolate, allowing the excess to drip off. Place the dipped heart onto a sheet of parchment paper.
Continue dipping the remaining hearts, working in small batches. The hearts become soft quickly when they are out of the freezer. If the chocolate cools and doesn't smooth out easily when dipping, reheat in 15 second increments to keep the chocolate smooth.
Allow the peanut butter heart coating to harden.
Heat white chocolate chips and teaspoon of shortening, working in 15-30 second bursts, until melted and smooth.
Transfer to a piping bag or small ziploc bag. Snip a very small hole in the bag and drizzle chocolate in large sweeps over the hearts to add accent drizzle. Immediately sprinkle with heart sprinkles if desired.