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One of the greatest battles in baking is to keep blueberries from sinking to the bottom of a muffin. Truth be told, there's not a lot that can be done—blueberries won't suddenly defy gravity when tossed in flour. I sidestep the problem by putting a scoop of plain batter in the bottom of each muffin cup before stirring in the blueberries, keeping the fruit well off the bottom with a physical barrier.
But why all this effort? Why all these preventative measures? What happens if we listen to what the blueberries have been trying to tell us all along and give them some prime real estate on the bottom of the pan? The answer: something amazing.
It’s only when we surrender to the will of the blueberry that its true purpose can be revealed: to be used in a giant upside-down muffin that’s cut into slices and served like a cake.
Of course, it's objectively not cake. It may look like one, but structurally speaking it has the same relatively low proportions of milk, sugar, and fat that define a traditional muffin. In fact, it's almost identical to my recipe for classic blueberry muffins, just reformatted for a cast iron skillet.
That means it's just as suitable for breakfast, and won't leave you buzzing with a sugar high. It has the same hint of coriander to amplify the blueberry flavor, the same pinch of nutmeg that makes butter seem more buttery, and the same butter-in-flour technique that minimizes gluten development to keep it tender and light. The only difference is an extra splash of milk to loosen the batter so it doesn't crown too high in the oven, a big squeeze of lemon over the blueberries to make the fruit layer more juicy and bright, and a pinch of zest in the batter since I've already got a lemon on hand.
The whole thing can be made in a stand mixer as per the original recipe, a method that combines all the dry ingredients together with butter up-front (essentially, the same technique we accomplish by hand when making biscuits or scones). But if you've got a food processor, the, uh, process is even faster.
Toss all the dry ingredients in a food processor, along with the butter and lemon zest, pulse until the butter disappears, then stir in the milk and eggs by hand (it's a little too easy to overmix the batter in the food processor). If you like, the bowl of buttery dry-mix can be left at cool room temperature overnight, for lightning fast muffin assembly in the morning.
Next, give the blueberries what they've always wanted: unobstructed access to the bottom of a pan—in this case, a 10-inch cast iron skillet, which happens to be the perfect size to accommodate an entire batch of muffin batter.
I'm all about using fresh blueberries for the fruit layer (I love how they retain their shape), but frozen blueberries are a-okay as well; since they've already lost their structure through the freeze/thaw process, their mushiness will make for a much jammier layer, but no adjustments aside from thawing need to be made. Either way, sprinkle with sugar, douse with lemon juice, and finish with a pinch of salt.
If you look closely, you'll see I've lined the cast iron skillet with parchment. It's a super low-effort way to ensure a clean release for the saucy, fruity layer when it's flipped, and a bit of added insurance for folks who don't have a well-seasoned skillet. Plus, it minimizes the fruity residue left in the pan, making it easier to clean up down the road.
On that note, let's take a moment to remember that a well-seasoned cast iron skillet isn't "seasoned" in the traditional sense. In the realm of cast iron, seasoning isn't flavor, it's a multi-layered barrier of polymerized oil that effectively makes cast iron non-stick. A cast iron skillet should never, ever impart any flavors or funky odors to baked goods; if it does, that means the skillet is dirty, so brush up on Daniel's guide to cleaning cast iron before getting started.
Those precautions out of the way, assembly is easy: blueberries on the bottom, batter on the top. The batter will look a little grainy from flecks of butter hardened by cold milk and eggs, but as with flakes of butter in a biscuit, those bits will melt in the oven.
Bake until the giant muffin is puffed, golden brown, and firm to the touch—about 45 minutes at 350°F. The exact time will vary dramatically depending on the cast iron's specific gauge, so (as with any recipe) the visual and textural cues will always take precedence over an estimated timeline. Forty-five minutes is a safe place to start, but if it's not done by then, keep checking it in 5-minute increments. An overbaked cake will be just as dry as an overbaked muffin.
Run a butter knife around the edge of the muffin-cake, invert a large plate over the top, and flip!
Wait about 30 seconds, then carefully remove the skillet. This will release a huge cloud of steam, so take care to keep your arm out of the way, or else be sure it's protected by clothing or a long oven mitt.
And with that, breakfast is served! With this recipe, there's no waiting around, so pour a cup of coffee, slice it up, and dig in.
Despite it's cake-like appearance, this breakfast is undeniably a muffin at heart. It's tender, light, and none too sweet or rich, so it doesn't weigh you down as a start to the day.
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