First things first, crank up that oven to 450°F (232°C). This temperature is crucial for achieving that perfect crispy exterior while keeping the insides light and fluffy.

In a large mixing bowl, whisk together 2 cups of all-purpose flour, 1 tablespoon of baking powder, 1/2 teaspoon of baking soda, 1 tablespoon of granulated sugar, and 1 teaspoon of sea salt. Make sure it's well combined. This mixture is the dry backbone of your biscuits.

Take that cold, unsalted butter and cut it into small cubes. Add these to your dry mixture. Now, using a pastry cutter (or your hands if you’re feeling adventurous), blend until the mixture resembles coarse crumbs. You want those little bits of butter to remain—this is what helps create the flakiness.

Make a well in the center of your flour mixture. Pour in 3/4 cup of chilled buttermilk, along with the optional lemon zest and vanilla extract. Mix until just combined. Be gentle here; over-mixing will turn your biscuits into hockey pucks. You want a soft, slightly sticky dough.

On a floured surface, turn out the dough. Pat it into a rectangle, about 1-inch thick. Fold the dough over itself a couple of times; this creates layers. Then, use a biscuit cutter to cut out your biscuits. Repeat until all the dough is used.

Arrange your biscuits on a baking sheet lined with parchment paper. Brush the tops with a little buttermilk. This helps them achieve that golden brown finish while baking.

Now, place your baking sheet in the preheated oven. Bake for 10-12 minutes, or until the biscuits are beautifully golden on top.