How to Make It
Preheat oven to 350°. Lightly grease the bottom and sides of a 10-inch cast-iron skillet.
Place miso in a large bowl; pour warm melted butter over miso and stir with a whisk to begin dispersing the miso paste. Add sugar, vanilla, and oil to bowl, whisking until ingredients are evenly combined. Add egg to bowl; whisk until combined and mixture is glossy.
Stir flour, baking powder, and salt into the miso mixture until fully combined. Spread the batter in an even layer in the prepared pan, smoothing surface with a rubber spatula. Sprinkle the surface with black and white sesame seeds to cover completely.
Bake at 350° for 20 to 25 minutes or until a toothpick inserted into the center of the blondie comes out clean. Cool completely; cut into wedges and serve.