Start by melting the chocolate chips in a non-stick pan or in the microwave. If you're using a pan, make sure the heat is on low or the chocolate will burn.
Once the chocolate is melted, spoon out the first layer of chocolate (about 1-2 tsp) to cover the bottom of the muffin tin.
Put the muffin tin into the freezer so the first layer can harden. This will take 3-7 minutes.
While the chocolate is setting in the freezer, mix together the protein powder and peanut butter.
Once the chocolate is set, spoon out 1-2 tsp of the PB filling on top of the chocolate. You can make this layer as thin or thick as you want!
After all the cups have the peanut butter layer, spoon out the rest of the chocolate on top (another 1-2 tsp). You may have to melt more chocolate chips.
Once the third layer is complete, put them back in the freezer to set for 15-20 minutes.
After the cups are set completely, you can take them out and store them in the fridge.