Preheat the oven to 375°F. Line a 12-well regular-size muffin tin with paper cups or spray the wells with oil. Set the tin aside.
Combine the flour, poppy seeds, baking powder, and salt in a medium bowl. Mix well and set aside.
Place a separate medium bowl on a folded kitchen towel. Add the aquafaba and, using a large whisk, whisk it until it is frothy, about 1 minute. Add the oil slowly while whisking to emulsify. Add the sugar in the same way. Add the milk, vanilla, lemon extract (if using), and zest and whisk well.
Add the flour mixture to the milk mixture and, using a wooden spoon, mix the batter until almost no more flour is visible. Lumps are fine; do not overmix.
Fill the wells about three-quarters full with the batter and sprinkle the coarse sugar on top. Bake the muffins until a toothpick inserted into the muffin in the middle well comes out clean, 17 to 20 minutes.
Cool the muffins on a cooling rack for 15 minutes before removing them from the tin. Cool the muffins completely before storing in airtight containers, where they will keep for a few days.
Notes
Note from the author: Although aquafaba is best if homemade using the recipe provided in the book, you can use aquafaba from canned chickpeas. Use the organic, low-sodium, canned chickpeas and strain off the liquid into a measuring cup using a fine mesh strainer. Note the amount of liquid you acquired, then add it to a medium saucepan and bring to a boil. Reduce to a simmer and cook until the liquid reduces by 1/3. Cool the aquafaba completely before using.Notes from Shannon: To turn these into vegan lemon blueberry muffins, I excluded the optional lemon extract, and the poppyseeds. I reserved one tablespoon of the mixed dry ingredients, and just before baking the muffins, I tossed the reserved dry mix with about 1/2 cup frozen blueberries and folded them very gently into the batter. If you want to use fresh blueberries, you needn't do this step with the flour, which is meant to stop the blueberries from discoloring the muffins.I originally tried to make these with coconut sugar in an effort to make them a little healthier, but they didn't come out that way. The texture wasn't as fluffy and with the 1:1 substitution they weren't sweet enough. More modifications would be needed to make these refined sugar-free and/or whole grain.