Soften the onions and garlic in a splash of oil with a pinch of salt. Cook on a medium low heat until they really break down and caramelise
Add the sugar, Worcestershire sauce and water. Cook the onions until they really break down and the liquid is nearly gone, allow to cool slightly and then add the miso stir through then blend until completely smooth.
Soften the butter and mix through the onion purée, store in the fridge
