Preheat oven to 450F/230C

Sift flour, sugar, salt, and baking powder together into alarge mixing bowl. Stir vinegar into milk and let stand 5 minutes.

Cut the cold butter into pea-size pieces andplace in the freezer if not using straight away. With a food processor or apastry cutter, work the butter into the flour mixture until it resembles coarsegravel.

Whisk milk and egg together in a small bowl. Add egg mixture to flour and stir until just combined. The mixture should be verysticky.

Turn dough onto a heavily floured surface andfold 10 - 15 times. With each fold incorporate the flour into the dough untilit’s dry but very soft. Use a bench scraper to scrape and incorporate thesticky bits back into dough.

Pat (don’t roll) dough into a rectangle 1-inchthick. Cut into 3-inch circles with a biscuit cutter or glass for roundbiscuits. Work leftover pieces into similar rounds. An alternative method is tocut dough into 9 squares with a knife.

Place biscuits on a baking sheet lined withsilpat or parchment paper. Put them into the oven and bake for 10 - 15 minutesor until their tops are golden brown. Brush the tops with melted butter whilethey’re still hot.