Greek Yogurt Lemon Poppyseed Muffins

white or white whole wheat flour

cornstarch

baking powder

salt

and 1/2 tablespoons poppyseeds

large eggs (separated (1 egg, 1 egg yolk))

lemon-flavored or vanilla-flavored Greek yogurt (not regular yogurt)

coconut oil (measured when melted)

heaping tablespoon lemon zest

lemon extract (no substitutes*)

brown sugar (lightly packed)

white sugar

lemon juice