Preheat the oven to 375 degrees F, and line a baking sheet with parchment paper.: As the oven warms you will notice a faint hum and the temperature stabilizing, which sets the stage for even rise and browning. A fully preheated oven ensures the scones begin to set around the edges right away, producing a tender interior and lightly golden bottom. If the oven is not hot enough the scones can spread and become dense, so allow at least ten minutes after the oven indicates it is preheated. Use an oven thermometer if your appliance tends to run cool, and line the sheet with parchment to prevent sticking and to make transferring easier.
Place the flour, sugar, lemon zest, baking powder, and salt in the bowl of a food processor, and pulse to combine.: The aromatic lift from the lemon zest will perfume the bowl as the dry ingredients mingle, and the pulsing creates a uniform distribution of leavening so the scones rise evenly. This step matters because unevenly distributed baking powder can cause patches of dense texture. One mistake is over processing into a flour like dust, which can lead to tough scones, so pulse briefly until ingredients are just blended and you can see the flecks of zest.
Cut the butter into pieces, and add it to the food processor. Pulse the food processor until the mixture resembles coarse meal. With the food processor running on low speed, stream in the cream.: When you add the cold butter pieces and pulse, you'll see the mixture break into coarse crumbs with pea sized bits of butter visible. Those little bits are crucial because they melt during baking and create steam pockets that produce flaky layers. Keep the butter cold to prevent it blending completely into the flour. A common error at this stage is using softened butter , which results in a uniform dough and dense scones.
When the dough has gathered itself into a ball, turn off the food processor and divide the dough into two equal portions. Gently knead the blueberries into each portion of dough.: As the heavy cream is added slowly you will notice the dry mixture begin to clump and hold together. This gradual addition prevents over hydration and gives you control over dough consistency. The correct texture is shaggy and slightly moist, not sticky and wet. If you add the cream too quickly you may end up with a gummy dough that will not rise properly.
Flatten each portion of dough into a disc shape, about 1 1/2-inches thick. Score each disc into 6 triangles with a knife, and pull the triangles slightly away from one another (allowing about 1/2-inch in between).: The dough should feel cool and slightly tacky when it forms a cohesive ball, with visible crumbs still present. Gently folding in the blueberries preserves their shape and prevents them from bleeding into the dough. Over working or vigorous kneading will crush the berries and can turn the dough purple and soggy, so use a light touch and fold a few times until they are distributed.
Bake the scones for 14 to 18 minutes, or until set in the centers and slightly golden on the bottoms.: As you flatten the discs you should feel a cool, dense texture that holds together. Scoring helps the scones bake into neat wedges and encourages uniform heat penetration. Leaving a small gap between wedges ensures air flows and the sides bake rather than steam. A common misstep is pressing the discs too thin, which can lead to overly crisp edges and a dry center, so aim for the recommended thickness.
Stir the powdered sugar and lemon juice together in a small bowl until smooth, and drizzle the icing over the scones.: While baking you will notice the kitchen fill with a warm, citrus berry scent and the tops developing a pale golden hue. Check the bottoms by lifting with a spatula to ensure a gentle golden brown; fully set centers will spring back slightly when touched. Baking too long will dry them out, and under baking leaves a gummy center, so test at the lower end of the time range and add a few minutes if needed based on your oven.
Stir the powdered sugar and lemon juice together in a small bowl until smooth, and drizzle the icing over the scones: The glaze should be glossy and pourable, with a bright tang from the lemon juice cutting through the richness of the scones. Drizzle when the scones are warm but not piping hot so the glaze sets nicely without running off. If the glaze is too thick add a touch more lemon juice , and if too thin add a pinch more powdered sugar. Avoid pouring over scalding hot scones or the glaze will become too runny and fail to adhere properly.
