Preheat the oven to 220°C. Line a baking tray with parchment paper. In a large bowl, whisk together the flour, baking powder, baking soda, salt, and sugar if using. Add the cold butter and work it into the flour with your fingertips or a pastry cutter until the mixture looks like coarse crumbs with some pea-sized butter pieces still visible. Pour in the cold buttermilk and stir gently just until the dough comes together. If it still looks very dry and crumbly, add 1 to 2 tbsp extra buttermilk. Do not overmix. The dough should look shaggy and slightly rough. Overworked biscuit dough makes tough biscuits instead of tender, fluffy ones. Keeping those visible, pea-sized pieces of cold butter throughout, rather than blending the fat in completely, is exactly what creates the pockets of steam responsible for a genuinely tall, flaky biscuit once baked.

Turn the dough out onto a lightly floured surface. Pat it into a rough rectangle about 2cm thick. Fold the dough over itself in thirds, then gently pat it out again. Repeat this 2 more times. Pat the final dough to about 2.5cm thick and cut out 8 biscuits using a round cutter, pressing straight down without twisting. Place them on the baking tray so the sides just barely touch for softer sides, or leave a little space for more crust. Those quick folds create layers. Twisting the cutter seals the edges and reduces the rise, so press straight down only. That repeated folding mechanically builds the same kind of distinct, stacked layers responsible for a biscuit's characteristic tall rise and flaky pull-apart texture — pressing straight down with the cutter, rather than twisting, protects those layers' cut edges from being sealed shut, which would otherwise trap them and prevent the biscuit from rising as freely.

Bake for 14 to 17 minutes, until well risen and lightly golden on top. Transfer to a rack or keep warm loosely covered. The biscuits should feel set, light, and fluffy inside. That real oven heat is what finally converts the dough's carefully preserved cold fat pockets into the steam responsible for the biscuit's actual rise — everything built into the dough up to this point exists specifically to make this stage possible.

While the biscuits bake, place a large skillet over medium heat. Add the breakfast sausage and cook, breaking it up with a spatula, for 6 to 8 minutes, until fully cooked and nicely browned in small crumbles. There should be some rendered fat in the pan. If the sausage is unusually lean and the skillet looks dry, add 1 tbsp butter before the next step. Let some of the sausage sit undisturbed long enough to brown. That deeper browning gives the gravy a fuller, more classic flavor. Allowing genuine, sustained contact between the sausage and the hot pan, rather than breaking it up constantly, is what lets real browning develop — that browning becomes a direct, foundational part of the gravy's own flavour in the very next stage.

Sprinkle the flour evenly over the sausage and stir well so the flour coats the meat and absorbs the fat. Cook for 1 to 2 minutes, stirring constantly, until the flour no longer looks raw. The mixture should look pasty but not dry. Cooking the flour directly in the sausage's own rendered fat, rather than adding it later to the milk, coats each starch granule and cooks out its raw taste at the same time — that combination is what allows the gravy to thicken smoothly once the milk joins, rather than tasting floury or turning lumpy.

Pour in the milk gradually, stirring constantly to prevent lumps. Once all the milk is added, keep cooking over medium to medium-low heat for 5 to 8 minutes, stirring often, until the gravy thickens. Season with black pepper generously, then add salt only if needed. Add cayenne if using. The gravy should be thick enough to coat a spoon and slowly flow over the biscuits, not stiff like paste and not thin like soup. If it gets too thick, loosen it with a splash of milk. Adding the milk gradually, rather than all at once, lets the flour-coated sausage properly absorb and thicken each addition before more liquid is poured in — dumping it in together risks the gravy turning lumpy rather than smoothly, evenly thickened.

Split the warm biscuits in half and place 2 biscuits per serving onto plates. Spoon the hot sausage gravy generously over the top so it settles into the biscuit crumb and pools slightly on the plate. Finish with a little extra black pepper and serve immediately. Splitting the biscuits while they're still genuinely warm, right before the hot gravy goes on, is what lets that gravy actually settle into the biscuit's own tender crumb rather than sitting as a separate layer on top of a cooled, less receptive surface.