Preheat oven to 325 F and make sure the rack is in the middle position. Prepare 2 baking sheets with parchment paper.
Turn the peanuts into a coarse crumb texture in a food processor. To the peanuts add the powdered sugar. Process again until you get a very fine crumb. Be careful not to over process or you will get peanut butter.
In a large bowl, mix together the flour, salt, and baking powder. Add the peanuts to the flour and mix until combined.
Drizzle into the mixture the melted butter and oil. Use your hands to knead the dough until it softens. If it feels too soft or greasy, refrigerate the dough for 15 minutes.
Roll the dough into 1 inch balls and place them 1.5 inches apart on the baking sheets. Flatten them gently with your palm, or if you want a decorative stamp use the cap of a marker.
Brush the top of the cookies with the egg. Bake the cookies for 20 to 22 minutes until lightly golden. Cool the cookies completely on a wire rack before serving.