Preheat the oven to 400°F (200°C). Position a rack in the center of the oven. If using paper liners, line a 12-cup muffin tin; if not, lightly grease each cup with nonstick spray or softened butter.

If using fresh blueberries or fruit, rinse and pat dry. If using nuts, toast lightly in a dry skillet for 3–4 minutes until fragrant, then cool. If using chocolate chips, measure and set aside.

Mix Dry Ingredients

In a large bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, and fine salt until evenly distributed and no lumps remain.

Mix Wet Ingredients

In a separate medium bowl or large measuring cup, whisk the eggs until blended. Add the whole milk, plain yogurt (or sour cream), melted butter, and vanilla extract (and lemon zest if making lemon muffins). Whisk until smooth and uniform.

Combine Batter

Make a well in the center of the dry ingredients. Pour the wet mixture into the well and gently fold with a rubber spatula or wooden spoon just until moistened. Do not overmix; some small streaks of flour are okay. Overmixing will make dense muffins.

If using mix-ins, gently fold them in now: for blueberries toss them with 1 tablespoon of flour before folding to prevent sinking; add chocolate chips or nuts directly. Reserve a few whole blueberries, chips, or nuts for topping each muffin if desired.

Portion & Top

Using a 1/3- or 1/4-cup scoop, divide batter evenly among the 12 prepared muffin cups, filling each about 3/4 full. Smooth tops lightly with the back of the scoop or spoon. Sprinkle reserved mix-ins on top and, if desired, dust with turbinado sugar for a crunchy top.

Bake & Check

Bake at 400°F (200°C) for 5 minutes, then reduce oven temperature to 375°F (190°C) without opening the door and continue baking for an additional 10–15 minutes, until muffins are golden and a toothpick inserted in the center comes out clean or with a few moist crumbs. (Total bake time ~15–20 minutes.)

Rotate the pan halfway through the second stage of baking if your oven has hot spots to ensure even browning.

Cool & Serve

Remove the muffins from the oven and let them cool in the tin for 5–7 minutes. Run a thin knife around the edges if needed and transfer muffins to a wire rack to cool another 15–20 minutes. Serve warm or at room temperature. Store cooled muffins in an airtight container for up to 2 days at room temperature or freeze for up to 3 months.