Peppercorn Sauce - Cooking like a Boss

3tbsp 0.045l 45ml 9tsp 0.19cup 0.079pint butter		fry until soft	reduce by half	simmer 15mins
3 small onion	finely chopped
3 clove garlic	smash and finely chop
450ml 0.45l 30tbsp 90tsp 1.9cup 0.792pint dry white wine
450ml 0.45l 30tbsp 90tsp 1.9cup 0.792pint double cream
6tbsp 0.09l 90ml 18tsp 0.38cup 0.158pint whole peppercorns	cracked in pestle and morter
1.5tsp 0.007l 7.5ml 0.5tbsp 0.032cup 0.013pint salt
3tsp 0.015l 15ml 1tbsp 0.063cup 0.026pint freshly ground pepper