In a large microwave safe bowl, melt the butter. Then add the brown sugar, powdered sugar, vanilla extract and stir by hand until combined (will look lumpy and strange). Then add the graham cracker crumbs and stir until combined. Finally, add the Nutella and peanut butter and stir until combined. Press the mixture into a sprayed 9 x 9 pan (for thinner bars, use a 9 x 13 pan but I prefer thicker bars). Place in freezer.
While the bars are cooling, make the chocolate frosting by melting the chocolate chips in a microwave safe bowl, taking care not to scorch them and checking every 15-30 seconds or so. After the chocolate chips are melted add in butter and cream and stir to incorporate. Then add powdered sugar and vanilla extract and stir to incorporate. If mixture becomes too thick to work with and the chocolate begins to set up, microwaving it again for 15 seconds will soften it.
When the frosting is ready, remove the bars from the freezer, frost them, and put bars back into the freezer to set up for a half hour before slicing them.
I store my sliced bars in the freezer or fridge in an airtight container and take them out about 20 minutes prior to eating. As they come up to room temperature, the flavor intensifies and they are more delicious and creamy but they will keep for weeks/months in the freezer as a make-ahead dessert.
Notes & Substitutions:
To make this vegan, replace all butter and cream with margarine and almond or soy milk. Rather than using Nutella use all peanut butter, use chocolate peanut butter that is vegan-safe, or add some cocoa powder to the nut butter of your choice.
To make this gluten free, use GF graham cracker crumbs.
If you don’t like Nutella, don’t have it, have a peanut allergy, want to use different ratios or types of nut butters, etc. feel free to try them. More than likely most substitutions will work just fine. You’re looking for approximately 1 to 1.5 cups of nut butter, total, in whatever type and combination you prefer.