Start by preheating your oven to 350°F (175°C). It’s essential to have the oven ready to go, as this helps the muffins bake evenly.

Line a standard muffin tin with paper liners. If you don’t have liners, you can generously grease the tin with butter or non-stick spray.

In a large mixing bowl, combine the softened unsalted butter and granulated sugar. Use a handheld or stand mixer to cream them together until the mixture is light and fluffy. This usually takes about 3 to 5 minutes. You want it to be airy!

Next, crack in the eggs, one at a time, beating well after each addition. Add the vanilla extract at this point as well. The mixture may look a bit curdled; that’s perfectly okay!

Stir in the sour cream and milk. Mix until just combined. We want a smooth batter, but be careful not to overmix!

In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, salt, and cinnamon. This will ensure that the leavening agents are evenly distributed throughout the flour.

Gradually add the dry ingredients to the wet mixture, stirring gently. Stop mixing as soon as you see no more flour; a few lumps are fine.

Now, gently fold in the fresh blueberries and lemon zest. Try not to squish the blueberries; you want them whole for that lovely burst of flavor.

Divide the batter equally into the prepared muffin tin, filling each cup about three-quarters full. This will allow room for the muffins to rise.

Pop the muffin tin into the preheated oven. Bake for about 20 to 25 minutes or until the tops are golden brown. A toothpick inserted into the center of a muffin should come out clean (a few crumbs are okay, but not wet batter).

Once baked, remove the muffins from the oven. Let them cool in the tin for about 5 minutes before transferring them to a wire rack to cool completely.