Prepare Your Pan and Oven: Preheat your oven to 350°F / 175°C.
Grease an 8-inch / 20cm round cake pan with butter, line the bottom with parchment paper, and grease the paper as well.
Grind the Peanuts: In a spice grinder or high-powered food processor, grind the 1 cup (240 ml) of roasted unsalted peanuts until they form a fine, flour-like powder. Be careful not to over-process, or you'll end up with peanut butter.
Mix the Batter: In a large mixing bowl, combine the self-rising flour and baking powder.
Add the granulated sugar, melted butter, eggs, and the finely ground peanuts.
Stir with a spatula or wooden spoon until all are just combined and the batter is smooth.
Bake the Cake: Pour the batter into your prepared cake pan and spread it evenly.
Bake for 25 to 30 minutes, or until a skewer inserted into the center comes out clean.
Cool Completely: Let the cake cool in the pan for 10 minutes before carefully inverting it onto a wire rack to cool completely. It's important the cake is fully cool before frosting.
Make the Frosting: While the cake cools, prepare the frosting.
In a medium bowl, use an electric mixer to beat the softened butter, crunchy peanut butter, and sifted confectioners’ sugar together until light, smooth, and creamy.
Decorate and Serve: Once the cake is completely cool, spread the peanut butter frosting evenly over the top. For a rustic look, use the back of a spoon to create swirls.
Sprinkle the crushed salted peanuts over the frosting before slicing and serving.
