Preheat oven to 375°F (190°C). Line a muffin tin with paper liners or lightly grease.
In a bowl, whisk together flour, baking powder, salt, and any dry add-ins (e.g., poppy seeds).
In another bowl, rub lemon zest into the sugar with your fingers to release oils.
Add eggs, melted butter (or oil), yogurt (or sour cream), lemon juice, vanilla, and optional lemon extract. Mix well.
Gently combine the wet and dry ingredients. Stir just until no dry streaks remain—do not overmix.
Fold in blueberries or other mix-ins, if using.
Scoop batter into muffin cups, filling each about ¾ full.
Bake for 18–20