Preheat the oven to 375 degrees F, and line a baking sheet with parchment paper.: The oven should be fully hot before the scones go in so they start rising immediately, creating a tender interior and a lightly browned exterior. You will notice a steady warmth in the kitchen and the oven will smell faintly of dry heat. A common mistake is putting scones into an oven that is still heating, which can yield dense centers. Make sure the rack is in the center position and the parchment is flat so the bottoms brown evenly.
Place the flour, sugar, lemon zest, baking powder, and salt in the bowl of a food processor, and pulse to combine.: Pulsing distributes the dry ingredients and the lemon zest so every forkful has bright citrus notes. You should hear quick, staccato pulses and see a uniform pale mixture. Avoid over-pulverizing which can heat the mixture and degrade the baking powder; short pulses are best.
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.: The sound will change to a softer, more continuous hum as the butter breaks down into pea sized bits. These little pieces are essential, they create steam pockets that give flakiness, and the cream binds without melting the butter. A trap is letting the butter warm too much, producing a greasy dough, so work quickly and keep the butter chilled.
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.: You will feel the dough hold together yet remain slightly tacky, and the blueberries should be folded in gently so they stay intact. Folding by hand prevents smashing the berries and keeps their juices from bleeding through the dough. If you overwork the dough it becomes tough, so use light, patient motions when integrating the fruit.
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 discs should feel cool and slightly dense when pressed, and scoring creates defined wedges that bake into individual scones. Pulling the wedges apart creates crisp edges and ensures even heat circulation. Avoid cutting too shallowly which can prevent proper separation, and be careful not to compress the dough when scoring.
Bake the scones for 14 to 18 minutes, or until set in the centers and slightly golden on the bottoms.: As they bake you will smell a warm, buttery aroma and see the edges turn a soft gold while the tops remain pale. Tap the center lightly, it should feel set but still springy. A common error is overbaking which dries the interior, so check at the shorter end of the time range and watch the bottom color; removing them too late will yield a drier scone.
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, clinging to the tops and settling into crevices. Use a spoon to create a thin, even drizzle that adds a bright finish without making the scone soggy. If the glaze is too thin it will run off, and if too thick it will clump, so adjust with tiny amounts of lemon juice or powdered sugar for the right consistency.