1. Preheat oven to 350 degrees F. Heavily butter a 9-inch cast-iron skillet. Whisk together the flour, salt, & baking powder. Whisk the eggs & sugar together. Add the butter & whisk until satiny. Stir in the flour mixture; whisk until smoothe.
2. Spread batter in the skillet & top with walnuts.
3. Bake 25 to 30 minutes, or until a toothpick inserted in the center comes out clean. Serve slightly warm or at room temperature.