Line a jelly roll or half sheet pan with parchment paper and set aside.
Using a hand mixer, beat together melted butter, peanut butter, granulated sugar, and vanilla extract until smooth and creamy.
Beat in powdered sugar.
Press peanut butter mixture into sheet pan spreading to about ½-inch thickness.
Place sheet pan in the freezer for 15 minutes.
Lift the parchment paper to remove the chilled peanut butter layer from the pan. Place a new sheet of parchment paper on the pan.
Use a cookie cutter to cut out ½-inch thick heart shapes from the chilled peanut butter layer.
Place cutouts on a parchment-lined sheet pan. Freeze for 30 minutes.
Scoop up the remaining peanut butter mixture, repress to ½-inch thickness, and cut out additional shapes.
After cutouts have chilled for 25 minutes, prepare the chocolate coating.
Place milk chocolate chips in a heatproof bowl. Dollop 2 tablespoons of shortening over the top. Heat and stir in 30-second increments in the microwave until the chocolate is smooth and melted completely.
Using a fork, lift one peanut butter cutout at a time and coat it completely with the melted chocolate. Tap excess chocolate off of the cutout and place it back onto the parchment paper.
Work in batches if the peanut butter cutouts become soft quickly.
Allow the chocolate to harden.
For optional drizzle, microwave white chocolate chips or chopped pieces and shortening (½ teaspoon per ½ cup) in 30-second increments until melted and smooth.
Scoop the melted chocolate into a plastic bag or piping bag. Snip a tiny corner off of the bag and drizzle in a zig-zag motion over the chocolate covered hearts. Immediately sprinkle with heart sprinkles.
Allow the chocolate to set for about 1 minute.