Preheat the oven to 375°F. Line a baking sheet with parchment paper.
In a small bowl, combine the lemon zest and sugar. Use your fingers to rub the zest into the sugar until it’s fragrant and slightly moist (this releases the lemon’s natural oils and boosts the flavor).
In a large mixing bowl, whisk together the flour, baking powder, baking soda, salt, and the lemon sugar mixture.
Add the cold, cubed butter to the dry mixture. Using your fingertips, work the butter in until the mixture looks shaggy, with thin, flattened pieces of butter visible throughout.
Pour in the heavy cream and mix gently with a fork or spatula just until the dough begins to come together. Turn it out onto a lightly floured surface.
Gently press the dough together with your hands just until it holds its shape. (It’s okay if it looks a little rough. This helps keep the biscuits light and flaky. Avoid kneading or over mixing.)
Pat into a rough 1-inch thick rectangle and cut into 4 sections. Stack the sections, press down gently, and reshape into a final rectangle about 10x5 inches, 1 inch thick. (This is a step I learned from Bon Appétit that helps to create beautiful, flaky layers.)
Slice into 8 equal squares and place on the prepared baking sheet. Sprinkle each biscuit with additional granulated sugar or sparkling sugar.
Freeze for 10 minutes or refrigerate for 20 minutes to help the biscuits hold their shape while baking.
Bake for 18–22 minutes, or until the tops are lightly golden and the edges are set. Cool slightly before serving.