There's a mix of cornmeal and all purpose flour in this batter, and that creates great texture as well as giving the muffins a beautiful look and color. You can make them with all purpose only, or a mix of apf and wheat, but they taste best with the cornmeal-all purpose combination. If you don't already have a sourdough starter, you can find my recipe here. You can use sourdough discard (from a mature starter) in this recipe, if you're looking to use it up, although a starter fed the day before will give you even better results. You can use frozen or fresh blueberries in this recipe. If using frozen, measure them out straight out of the freezer. Even if you use cupcake liners in your muffin tin, be sure to spray or brush on some oil on the insides of the liners. I didn't, and crumbs stuck to the liner. We could pull them off quite easily, but save yourself the trouble, if possible. This is a fairly thick batter, and that's okay. You can use a spoon or cup measure to scoop it into the muffin cups. But if you find that it's too dry, or has dry flour that won't mix in, you can add a little more nondairy milk.