Combine the flour, milk, vinegar, and rapadura. It will be the consistency of a thick batter. Cover and let sit for 12-24 hours.
Mix, recover, and allow the batter to sit for another 2 hours.
Generously flour a baking sheet. Then, generously flour your hands.Then, punch down the dough and knead it slightly, adding a teensy bit more flour if you need to keep it from being too gooey.Gently divide the dough into 8-11 ‘muffins'. I find it best to simply work each muffin a bit in my hands with a wee bit of flour to get it to the correct shape. Don't worry about getting it perfectly smooth or perfectly shaped. It's not going to matter in the end.Let them sit for 20 minutes and recover from the massage you just gave them Heat up a cast iron skillet (or skillet of choice) on medium-low heat. Gently transfer a few muffins at a time to the pan. It can be hard to move them, they're sort of gooey. But just be gentle, work with your floured fingertips, and you'll do fine. If it's super funky by the time it gets into the pan, just reshape it a bit with your fingertips. And be careful to not overcrowd them in the pan. They will puff up and expand as they cook. The goal in this step is NOT to cook the muffins completely, but rather to brown the outsides. So give them about two-three minutes per side and then transfer them back onto the floured baking sheet.Don't worry about the dough in the middle. We'll bake that out.Repeat the browning stage with all the muffins. This should take just ten or fifteen minutes.
Bake the muffins in a preheated 325 degree oven until they are cooked thoroughly (about another ten to fifteen minutes is all). You'll know when they're ready because your kitchen will begin to smell like heaven.