Cook the sausage (500g) in a large frypan. Once cooked, remove from the pan and let cool slightly. Slice into 1cm pieces. Leave sausage fat in the pan.
To the sausage fat, add sliced onions (1) and fry until slightly brown. Add flour (1/4 cup or 35g) and cook for 1 minute until the fat absorbs the flour. Add pepper (1 tsp).
Add milk (2.5 cups) slowly in 1/2 cup batches to let the roux absorb it slowly. Feel free to adjust the thickness of the gravy by adding more or less milk.
Check seasonings and add salt if necessary.
Biscuits
Preheat oven to 425°F/210°C
In the bowl of a food processor with a blade attachment, add flour (2.5 cups), baking powder (2 Tbsps), and salt (1 tsp). Lightly mix.
Add butter (1/2 cup) and blend until pea-size clumps form.
With motor running very slowly, add buttermilk (1 cup) into the well. Mix gently with a fork until just combined (don't overmix, it will make tough biscuits).
Turn the dough out onto a floured surface and create a rectangle using your hands. If it's flaky, just keep pressing the dough into the right shape, it will come together eventually.
Fold the dough into thirds (like folding a letter). (Fold left side over center, then right side, so it's still in a rectangular shape.) Then roll back out to 1-inch thick. Repeat the folding and rolling process twice more, rolling the dough out to ½" thick on the final time.
Cut the rectangle into 9 or 12 squares. Soften the edges and place on a baking paper lined baking sheet about 1-inch apart.
Bake for about 13-15 minutes until cooked through and golden brown on top.