Position a rack in the middle of the oven and preheat to 325 degrees F. Line a 8 by 8-inch baking pan with foil letting long flaps overlap on each side. Spray foil with nonstick spray.
Break up the brown sugar to remove all lumps. In a standing mixer with the paddle attachment, beat the cream cheese and sugar on medium speed until very smooth. Add the cream and beat slowly; then add the yolks and vanilla mixing until just combined. Gently stir in peanut butter. Take care not to over beat the mixture; this incorporates too much air and causes the cheesecake to crack.
Pour and evenly spread the batter in the prepared pan. Bake for 15 minutes. Open the oven to release some heat, then lower the temperature to 200 degrees F. Continue to bake the cheesecake until the outside is set but the center is still loose, for about 45 minutes. Turn off the oven, and cool cheesecake in the oven for 45 more minutes. Cover and refrigerate at least 8 hours or overnight.
Lift cheesecake from the pan by lifting up the foil. Transfer to a cutting board. Cut into
1 1/2-inch cubes. Stick a wooden pop stick halfway into each bar and freeze for 1 hour.
Meanwhile, put the shortening and chocolate in a medium heatproof bowl. Bring a saucepan filled with an inch or so of water to a very slow simmer; set the bowl over, but not touching, the water. Stir the chocolate occasionally until melted and smooth. Remove from the heat and let cool slightly. (Alternatively, put the chocolate in a medium microwave-safe bowl. Melt at 50 percent power in the microwave until soft, about 1 minute. Stir, and continue to heat until completely melted, about 1 minute more.)
Dip the pops into the chocolate mixture, and stand on waxed paper to set, about 5 minutes. Serve cold (straight from the fridge), or freeze up to 2 weeks. Frozen pops make a cool summer treat, or can be allowed to temper for 10 minutes at room temperature before serving.
Upgrade: Coat the pops with chopped nuts or candies for a really decadent finish. To do this let the dipped pops drip over a bowl for 15 seconds before rolling them.