Onion and red wine vinegar sauce for beef, emu, kangaroo or venision

This is a very simple sauce for red meat.

Ingredients:

1 onion, sliced
2 cloves garlic, crushed
2 tbs red wine vinegar
1/2 tsp whole mustard seeds
freshly ground black pepper
sea salt
olive oil

Heat some olive oil in a small fry pan. Add the mustard seeds. When they start to pop, add the onions and garlic. Fry for five minutes, then add the red wine vinegar. Season to taste with freshly ground black pepper and sea salt. Simmer until onions are very soft. Transfer everything into the bowl of a food processor and blitz until smooth. Drain sauce to remove excess liquid and then spoon a small amount next to each piece of meat.