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.
Use your fingers to press down the mixture, evenly spreading it 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 bunny and/or egg shapes from the peanut butter sheet.
Place the cut shapes onto a sheet of parchment paper and place them back into the freezer.
After the cutouts have chilled for 25 minutes, prepare the chocolate for dipping. (Details on website recipe).
Remove just one or two chilled peanut butter bunnies/eggs from the freezer at a time. Use a fork to dip the cutout into the melted chocolate and flip it to coat both sides. Lift from the chocolate, allowing the excess to drip off. Place the dipped shape onto a sheet of parchment paper.
Allow the chocolate coating to harden. Heat dark 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 bunnies and eggs to add accent drizzle.
Allow chocolate to set (about 1 minute).