Peppercorn Sauce - Cooking like a Boss

2 ¹⁄₂tbsp 0.037l 37 ¹⁄₂ml 7 ¹⁄₂tsp 0.159cup 0.066pint butter		fry until soft	reduce by half	simmer 15mins
2 ¹⁄₂ small onion	finely chopped
2 ¹⁄₂ clove garlic	smash and finely chop
375ml ³⁄₈l 25tbsp 75tsp 1.59cup 0.66pint dry white wine
375ml ³⁄₈l 25tbsp 75tsp 1.59cup 0.66pint double cream
5tbsp 0.075l 75ml 15tsp 0.317cup 0.132pint whole peppercorns	cracked in pestle and morter
1.25tsp 0.006l 6.25ml 0.417tbsp 0.026cup 0.011pint salt
2 ¹⁄₂tsp 0.013l 12 ¹⁄₂ml ⁵⁄₆tbsp 0.053cup 0.022pint freshly ground pepper