Preheat oven to 425°F. Line 12 standard muffin cups with paper liners or spray with nonstick cooking spray.: Warmth in the oven is noticeable immediately as it begins to glow, and the preheated air helps the batter set at the edges so the muffins rise tall and domed. You may hear a faint hum from the oven as it stabilizes and feel that first blast of heat when you open the door. This initial high temperature jump starts the rise before the interior fully sets, which is essential for a tall crown. A common mistake is skipping liners or not prepping the tin, which can lead to sticking or uneven browning. Make sure the oven truly reaches temperature before you pop the muffins in, and line the wells to ensure easy release.
In a large bowl, add the lemon zest, granulated sugar and brown sugar. Mix the ingredients together with your fingertips until the sugar is moistened and fragrant.: Right away you will notice the scent of citrus lifting from the bowl as the oils release from the lemon zest , and the sugars will feel slightly damp between your fingers. Rubbing the zest into the sugars intensifies the aroma, and the mixture will glisten as tiny specks of zest are coated. This step infuses the batter with a bright foundation of flavor, which is why it is worth the few moments it takes. Avoid overworking the sugar or you may make it too wet, which can affect how it integrates with the dry ingredients later. If the sugar seems too clumped, fluff it gently with a fork.
To the sugar mixture, add the flour, baking soda and salt. In another bowl, combine the egg, lemon juice, buttermilk and oil. Create a small well in the dry ingredients, pouring the wet ingredients into the well and stirring just to combine. Gently fold in the raspberries.: When you sift or whisk together the all-purpose flour , baking soda , and fine sea salt , the mixture takes on a lighter, more even texture. Separately, whisk the egg , lemon juice , buttermilk , and vegetable oil until smooth, and notice the silky sheen the oil brings. Pouring the wet into a well keeps the ingredients from clumping and encourages a gentle incorporation. As you fold in the fresh raspberries , do it with soft motions so they remain intact and don’t turn the batter uniformly pink. You will see little islands of fruit rather than streaks of color. The rationale here is minimal mixing to protect tenderness, and a typical error is vigorous stirring which activates the gluten and yields dense muffins.
Divide batter evenly into the prepared muffin wells. The wells will be very full. Sprinkle the tops with coarse sugar.: As you portion the batter, it should mound high in each cup, almost to the brim, which is the cue for those bakery style domes. Using a cookie scoop set or spoon helps maintain uniformity so the muffins bake evenly. When you sprinkle coarse sugar on top, it settles into the batter and gives a sparkly crust after baking. If the wells are underfilled, the muffins will be flat and less dramatic, so resist the urge to make smaller portions. Overfilling can cause overflow, so aim to match the suggested volume. A frequent oversight is uneven scoops, which causes some muffins to be done sooner than others.
Bake at 425°F for 10 minutes. Leaving the oven door closed, set the oven temperature to 350°F and continue to bake for another 7-9 minutes, until the tops are golden and a toothpick inserted into the center comes out clean.: The first burst at 425°F produces a rapid exterior set and visible dome growth, and during those ten minutes you will see the tops puff and gain color. When you quietly change the temperature to 350°F without opening the door, the muffins finish cooking through without browning too aggressively. The internal crumb should feel springy and a toothpick will emerge with just a few moist crumbs. Smell is a good guide here, you will notice a fragrant citrus and baked fruit aroma when they are nearly done. A common pitfall is opening the door during the high temp stage, which can cause the domes to collapse, so resist peeking.
Let muffins cool in the pan for about 5 minutes before removing them to a wire rack to finish cooling.: The muffins will be very tender when hot, and letting them rest in the pan allows the interior to set and prevents tearing when you remove them. In those minutes you will feel a gentle release of steam, and the tops will firm slightly while the centers stabilize. Transferring too soon risks collapse or sticking to the pan, while waiting too long can trap moisture and soften the bases. Use a thin spatula to loosen edges if needed, and move them to a wire rack so air circulates and they cool evenly. Patience here preserves texture.