In the bowl of a standing mixer or with an electric mixer, combine all the ingredients for the peanut butter layer. It should be stiff but not dry. Press it into a 9 x 13 -inch pan with your fingers. You can smooth it out with a flat spatula if you like.
Ritz Crunch and Chocolate Ganache
For the Ritz crunch, preheat the oven to 275 degrees. Line a cookie sheet with a slipat or waxed paper. Empty the crackers into a bowl, crush them with your hands and mix them with the sugar, milk powder, and salt. Pour the melted butter over the the crackers mixture and mix it together. It should remind you of streusel sized crumbs. Spread the mixture on the cookie sheet. Bake for 20 minutes. Set aside.
For the ganache, put the chocolate into a glass bowl. Whisk the cream and creme fraiche together in a pyrex or other microwave safe container, and heat for 1-2 minutes, until steaming. Pour the cream mixture over chopped chocolate and let it sit for about 2 minutes. Whisk together until glossy. Add vanilla and give it a stir.
To finish assembly: Pour the ganache over the peanut butter layer, smooth it to the outer edges. Sprinkle the ritz crunch over the top, crumbling it as you go if the pieces seem too big. Put in the refrigerator for about an hour, until the ganache is slightly set. Cut into small squares and serve.