Upside-Down Blueberry Muffin Recipe

Adjust oven rack to middle position and preheat to 350°F (180°C). Line a 10-inch cast iron skillet with parchment paper and set aside. Combine flour, sugar, baking powder, lemon zest, salt, baking soda, coriander, nutmeg, and butter in the bowl of a stand mixer fitted with a paddle attachment. Mix at low speed to form a mealy powder, about 2 minutes. If you like, this "mix" can be held overnight at cool room temperature in an airtight container. To proceed, transfer to a large bowl and stir in the milk, eggs, and vanilla (if using).

Transfer blueberries to the parchment-lined skillet and shake gently to distribute in an even layer. Sprinkle with sugar, lemon juice, and salt. Dollop batter over the surface as evenly as possible, then smooth with an offset spatula. Bake until muffin is puffed and golden brown, about 45 minutes. The exact bake time will vary depending on the skillet's gauge, so keep a close eye on it to prevent overbaking.

To serve, run a dull knife around the edge of the pan to loosen the muffin, invert a large plate or platter over the top, and flip. Wait about 30 seconds, then remove the cast iron skillet, taking care to avoid the cloud of steam it will release. Cut generous wedges and serve immediately, as leftovers will stale rapidly overnight.