Combine the yeast and water in the bowl of a stand mixer outfitted with the dough hook and whisk together to dissolve the yeast. Nuke the buttermilk in the microwave for 20 to 30 seconds, or warm it over low heat in a small pan on the stovetop just until it loses the refrigerator chill; you’re not really heating the buttermilk, but ensuring that chilly milk won’t retard the dough’s rise. Stir the no-longer-cold buttermilk into the yeast and water. Add the flour, sugar, and kosher salt to the bowl, turn the mixer on to low/medium-low speed, and process just until it comes together as a shaggy, droopy dough 3 to 4 minutes. With the mixer still running, add the butter to the dough a tablespoon at a time. (Make sure it’s at room temperature—you’ll overwork the dough trying to incorporate cold butter into it.) The dough will look as if it is separating, and from this point on it will hang out at the bottom of the bowl, reaching up the dough hook like an appendage of the sandman but never fully coalescing into a ball again. Knead it for 7 to 8 minutes, by which time it should be tacky but no longer sticky and hold its shape. Lightly spray a large mixing bowl with oil. Using a rubber spatula, scrape the dough from the mixer bowl into the greased bowl. Cover with plastic wrap and leave the dough to rest, relax, and rise (though it doesn’t rise so much as it expands in the bowl) for 1 hour. After the dough has risen, put it into the refrigerator for 30 minutes to 1 hour to chill, to make it easier to handle. While the dough’s resting, line a couple of rimmed baking sheets with parchment paper and cover them each with a ¼-inch-deep layer of cornmeal, into which you will nestle your muffins. (That’s way more cornmeal than will stick to the muffins, but whatever’s left over will be fine to use in another recipe.) Scatter your work surface with a very, very fine dusting of flour, and very lightly flour your hands. Turn the dough out onto the work surface and knead it a few times to deflate it. Shape it into a fat, smoothish log. For traditional-size English muffins, pinch off pieces about the size of a handball (which should weigh about 60 grams). With lightly floured palms, roll the pieces of dough into neat balls, applying as little pressure as possible. The dough should be pillowy and tender and delicate and have the tiniest bit of spring to it. As you shape them, transfer the balls of dough, one by one, to the baking sheet: Nestle each ball of dough into the cornmeal, then pat it down gently so some of the cornmeal adheres to the bottom of the future muffin, grab the ball very gently by its sides (the parts you don’t want cornmeal on), and flip it over, gently patting the cornmealed top so the bottom picks up some of the cornmeal. Leave about an inch between the muffins, giving them enough space to stretch and rise as they may need. You can proceed with the recipe directly, or you can wrap the baking sheets of proofing dough in plastic wrap and put them in the fridge to chill for 30 minutes, after which time the muffins will be easier to handle. You can also take a longer break: wrapped and refrigerated, the muffins will keep (and improve) for up to 3 days. Turn the oven on to 250°F. Warm a cast-iron skillet or griddle over the lowest heat setting possible for 5 or so minutes. You should be able to comfortably hold your hand very close to the pan and just feel some radiant heat—nothing that would make you want to pull your hand back. Scatter the pan with a thin, even layer of cornmeal and warm for a minute more. Grab the proofed muffins one by one by their uncornmealed sides, dust off any excess cornmeal clinging to their tops and bottoms (you want a thin even coating, not a thick jacket), and transfer them to the pan, working in batches. This is the all-important nook-and-crannies-forming stage of English muffin cookery: you want the muffins to rise and griddle-bake slowly. You almost can’t take enough time with this stage. (And if any point before the final couple of minutes of cooking you smell cornmeal toasting or browning, instead of just warming, turn the heat down.) After about 4 minutes, their tops will begin to puff and dome: that’s your cue to flip them. Use a small offset spatula to flip them if you have one (and buy one to do so the next time if you don’t—your fingers will leave prints). After 4 or 5 minutes on the second side, the bottoms of the muffins should still feel airy and light. Once they’re at that point (you may have to gently cook and gently flip them one more time before they get to the handleably delicate stage), you can nudge up the heat slightly, and turning them every 2 to 3 minutes, toast their tops and bottoms. (Here the smell of toasting cornmeal is okay.) When the muffins are toasted—tops and bottoms mottled with brown, but mainly golden—transfer them to a baking sheet, and put them in the oven for 10 minutes—transfer them to a baking sheet, and put them in the oven for 10 minutes to finish baking. Remove from the oven and let them cool on the baking sheet until they reach room temperature. Use the tines of a fork to puncture an equator of tiny holes around the middle of each muffin, and then pry them apart into two halves. The muffins are ready to be seared (with a light spread of butter) and spread with pickled strawberry jam!