Evenly spread grated butter on a baking tray and freeze for 20 minutes.
Combine flour, baking powder, and salt in a large bowl. Sieve to mix well. Add frozen butter and, using your hands, rub the mixture together for 2 minutes to create pea-size balls.
Whisk together lemon juice, 1 cup heavy cream, and egg in a separate bowl. Pour into the flour mixture. Hand-mix for a few minutes until loosely combined. Fold in cheese and lemon zest.
Place dough on a floured work surface and gently knead. Don’t overmix.
Roll out dough into an 8-inch circle, roughly 1-inch thick. Wrap in cling wrap and refrigerate for 30 minutes.
Heat oven to 375°F.
Once chilled, cut dough into 6 triangle pieces. Place on a parchment lined–baking tray and brush each with the remaining heavy cream.
Bake for 20 to 25 minutes, or until a toothpick inserted into the center of each scone comes out clean.
Remove from oven and cool on a rack for 30 minutes.