The doughnut muffin is a tour de force of a morning pastry, packing in the best of both worlds: a dense, cakey muffin with a crispy, doughnutlike sweet crust which is achieved by brushing the muffin all over with butter and dousing it in powdered sugar just after it comes out of the oven. It's like eating a doughnut and a muffin all at once, in the best way possible.