Preheat oven to 375°F (190°C). Generously coat a mini muffin pan with cooking spray. Make sure the eggs, sour cream, and milk are at room temperature before starting. This helps the batter mix smoothly and keeps it from curdling.
In a medium bowl, add the eggs. Whisk. Add the remaining wet ingredients and whisk until smooth and emulsified.
In a separate, larger bowl, combine the flour, baking powder, cornstarch, salt, and mini chocolate chips. Stir to mix.
Pour the wet ingredients into the bowl with the dry ingredients. Whisk together until combined. Use a spatula to scrape the edges of the bowl. Be careful not to overmix.
Spoon the batter into the prepared muffin tin, filling cavities nearly to the top. Bake for 10–13 minutes, or until a toothpick inserted into the center of a muffin comes out clean or with a few moist crumbs. Remove the muffin tin from the oven and let it cool for 5 minutes. Gently remove the muffins from the tin and place them onto a cooling rack. Allow the muffins to fully cool on the rack. If baking in batches, re-grease the pan before adding more batter.
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Notes
Note 1: The key to nailing the perfect muffin texture is all about the flour. If you pack in too much, you’ll have dense/dry muffins. My tip? Place your mixing bowl on a food scale and spoon in the flour until you hit 225 grams. It's faster and more accurate than measuring cups! If you don’t have a food scale, spoon the flour into the measuring cup, then use the back of a butter knife to level off the top.Note 2: Muffin variations: For the variations below, omit the mini chocolate chips unless you want a chocolate-chip version.
Blueberry Muffins: Large blueberries might overpower the mini muffins. Use frozen wild blueberries, which are much smaller in size. After preparing the batter, add it to the muffin cavities and then top each with about 6–8 wild blueberries. Swirl them into the batter using a toothpick. (For an extra burst of flavor, you can add some lemon zest to the muffin batter and replace 1 teaspoon vanilla with 1 teaspoon lemon extract.)
Cinnamon Sugar Muffins: Add 1 teaspoon ground cinnamon to the dry ingredients, then bake the muffins as directed. For the topping, melt 6 tablespoons butter. In a separate bowl, mix together 1/3 cup brown sugar and 4 teaspoons cinnamon. Dip the tops of the baked muffins into the melted butter, then into the cinnamon-sugar mixture.
Mixed Berry Muffins: Follow the recipe to prepare the batter. Next, pulse 1/2 cup of frozen mixed berries in a food processor until they’re broken into small pieces. Distribute the batter into the muffin cavities and spoon the crushed berries over each. Using a toothpick, gently swirl the berries into the batter. Bake as instructed, but allow a few extra minutes due to the cold berries.
Storage: Store at room temperature in an airtight container for 2–3 days or in the fridge for up to a week. Freeze on a sheet pan and store in a freezer bag for up to 3 months.