1. Preheat the oven to 350°F (fan-assisted convection) and line a baking tray with parchment paper.
2. In a large bowl, stir together the peanut butter, flour, sugar, salt, baking powder, and peanut oil with a spatula until the dough comes together and there are no streaks of flour. The dough should be thick but malleable. If it sticks to your hands, add a bit more peanut oil to it, one teaspoon at a time.
3. Divide out the dough into 2 teaspoon-portions (about 12 grams each). You should end up with around 35 pieces. Roll a piece of dough in the palms of your hands to shape it into a ball, then place it on the prepared baking tray. Repeat with remaining dough leaving at least a 1-inch gap between each ball. (They won’t expand too much but this is just to make sure there’s good airflow and the cookies bake evenly.)
4. Press a roasted peanut into the center of each dough ball, which should flatten each cookie a little. Brush a light coating of beaten egg over each cookie.
5. Bake the cookies for 16-18 minutes, until they’re nicely bronzed, just a shade darker than the peanut butter you started out with. When they’re done baking, remove from the oven and let it cool on the tray for 10 minutes before eating.