Preheat oven to 400°F. Line a baking sheet with parchment paper.: As the oven warms, you should notice a faint electrical hum and a gentle rise in the kitchen heat, creating the ideal environment for a rapid oven spring. Preheating ensures the scones begin to set immediately on contact, producing crisp edges. A common mistake is not preheating long enough, which leads to flat, dense scones, so wait until the oven reaches a steady temperature before baking.
In a medium bowl, combine sugar and lemon zest; mix with your fingertips until the sugar is moistened and fragrant. Add in the flour, baking powder and salt and mix until combined.: Rubbing the lemon zest into the sugar releases citrus oils, and you should smell a bright, tangy perfume as you work. When the dry ingredients are mixed, the flour will look homogenous and slightly grainy, ready to accept the butter. Avoid overmilling the zest into tiny pieces that could create bitter bits, and don’t overwork the flour mixture which can develop gluten and yield tougher scones.
Grate butter into flour mixture on the large holes of a box grater; use a fork or pastry blender to work in the butter until the mixture resembles coarse meal.: As you grate frozen unsalted butter , you’ll hear a soft scraping and see small flakes scattered through the flour, like snow. Working the butter until the mixture looks like coarse cornmeal is key for pockets of flakiness after baking. If the butter starts to warm and smear, chill the bowl briefly because warm butter will coat the flour and prevent proper aeration, producing dense texture.
In a small bowl, whisk the yogurt (or sour cream), egg and vanilla until smooth.: Whisking brings a sheen to the mixture, with the egg stretching the liquid into a glossy emulsion. The blend should be homogenous, with no streaks of white or yolk visible. If the yogurt is too cold and clumpy, let it sit a minute to loosen, because uneven liquid can cause pockets of dryness in the dough.
Using a fork, stir sour cream mixture into flour mixture until a dough starts to form. Gently fold in raspberries. The raspberries may break up a little, no worries because they’ll bake up beautifully. Gently use your hands to press the dough against the bowl into a ball. The dough will be quite sticky at first, but it will come together.: When you begin stirring, listen for soft scraping as the wet and dry components meet, and watch the dough take on a slightly glossy sheen. Folding in the fresh raspberries should be done delicately to avoid complete disintegration; a little color streaking is okay. If you press too hard or overmix, the raspberries will release too much moisture, making the dough soggy, so use gentle strokes until you have a cohesive mass.
Place the dough on a lightly floured surface and pat into a 7-inch circle about 3/4-inch thick. Use a knife to cut into 8 triangles; place on prepared baking sheet, about 1 inch apart. Bake until golden, about 15 to 17 minutes. Cool for 10 minutes and prepare the glaze.: As you pat the dough, the surface should feel tacky but manageable, and the circle will hold its shape. The triangles will brown at the edges and develop a warm, golden color in the oven, offering a visual cue that interior crumb is set. Overbaking will dry them out, so check a few minutes before the lower end of the time range to avoid overly firm centers. Allowing a 10 minute cool period stops carryover cooking and gives the scones a chance to settle, preventing the glaze from slipping off.
In a medium bowl, prepare the glaze by mixing together the melted butter, confectioners’ sugar, vanilla and lemon juice. Whisk until smooth. Dip the top of the scones into the glaze and allow the glaze to harden. If you would like to drizzle the glaze onto your scones instead of dipping them, you can thicken the glaze a bit with additional confectioners’ sugar.: The glaze should be glossy and pourable, with the scent of lemon and vanilla rising as you whisk. Dipping creates a uniform sheen and a satisfying crack when the glaze hardens; drizzling gives a more rustic look. If the glaze is too thin it will run off and pool on the tray, so add more sifted sugar to thicken if needed. Let the glaze set in a cool spot, and resist the urge to stack scones until the coating is fully firm.