In a large mixing bowl, combine the softened butter, salt, baking powder, and powdered sugar, then beat with a mixer until creamy. Add the egg and mix again until fully incorporated.
Gradually add the sifted flour and knead just until you get a soft dough. The key in this recipe is not to overwork the dough or knead it too hard, so you do not need to add any extra flour.
Wrap the dough in plastic wrap and place it in the freezer for 30 minutes. Take the dough out, lightly flour your work surface, and roll it out into a thin sheet about 8 mm thick.
Use a cookie cutter or a glass to cut out circles, then cut a small circle in the center of each one to form rings.
Arrange the rings on a baking sheet lined with parchment paper, brush the tops with the beaten egg, and sprinkle the chopped peanuts generously over the cookies.
Place the cookies in a preheated oven and bake at 350°F (180°C) for 25–30 minutes, until lightly golden around the edges.