Preheat your oven to 425F (220C) and line a 12-count muffin tin with paper liners. Set aside.

In a large mixing bowl, whisk together flour, sugar, baking powder, baking soda, cornstarch, and salt.

In a separate bowl, whisk together sour cream, melted butter, egg, lemon juice, lemon zest, and lemon extract (if using) until well-combined.

Add the wet ingredients to the dry ingredients and use a spatula to gently combine until you have a uniform batter (don’t over-mix or your muffins will be dense!). This is a very thick muffin batter.

Evenly divide batter into prepared muffin tin – for larger, taller muffins only divide the batter into 10 cavities rather than all 12.

Bake in center rack of 425F (220C) for 8 minutes, then, without opening the oven door, reduce temperature to 350F and continue to bake for another 5-6 minutes (may need a minute longer if only baking 10-12 muffins), unti a toothpick inserted in the center of a muffin comes out clean or with a few moist crumbs.

Allow muffins to cool in their pan for about 5-10 minutes before carefully removing from pan and allowing to cool on cooling rack before adding glaze.

Whisk together powdered sugar and 1 ½ Tbsp lemon juice. If glaze is too thick to whisk easily, add more lemon juice, a splash at a time, until a smooth consistency is reached that drizzles off the whisk in a ribbon.

Drizzle over muffins or dip completely cooled muffin tops in the glaze.

If you’re the patient type, allow glaze to sit and become firm before serving.