Peppercorn Sauce - Cooking like a Boss

1tbsp 0.015l 15ml 3tsp 0.063cup 0.026pint butter		fry until soft	reduce by half	simmer 15mins
1 small onion	finely chopped
1 clove garlic	smash and finely chop
150ml 0.15l 10tbsp 30tsp 0.634cup 0.264pint dry white wine
150ml 0.15l 10tbsp 30tsp 0.634cup 0.264pint double cream
2tbsp 0.03l 30ml 6tsp 0.127cup 0.053pint whole peppercorns	cracked in pestle and morter
0.5tsp 0.003l 2.5ml 0.167tbsp 0.011cup 0.004pint salt
1tsp 0.005l 5ml ¹⁄₃tbsp 0.021cup 0.009pint freshly ground pepper