01 - Preheat oven to 425°F. Line a baking sheet with parchment paper.
02 - Cook diced Chinese sausage in a skillet over medium heat for 2–3 minutes until fragrant and lightly browned. Drain excess fat and let cool completely.
03 - Whisk together flour, baking powder, baking soda, salt, and sugar in a large bowl.
04 - Add cold diced butter to flour mixture. Using a pastry cutter or fingertips, cut butter into flour until mixture resembles coarse crumbs.
05 - Stir cooled sausage, scallions, and sesame seeds into flour-butter mixture.
06 - Pour in cold milk and mix gently until shaggy dough forms. Do not overmix.
07 - Turn dough onto lightly floured surface. Pat into 1-inch thick rectangle. Fold dough in half, pat out again, and repeat once more for flaky layers.
08 - Cut out rounds using a 2.5-inch biscuit cutter. Gather scraps and repeat, handling dough as little as possible.
09 - Place biscuits on prepared baking sheet. Brush tops with beaten egg if desired.
10 - Bake for 16–18 minutes until golden brown. Cool slightly before serving warm.