Creamy onion sauce

I wasn't sure how this onion sauce would turn out, but it was a massive success with hubbie and children. Even my sauce-hating son liked it! Brilliant as an accompaniment or sauce with BBQ or as we ate it-with oven baked salmon, broccoli, breaded and fried courgette, asparagus and green beans (and potato mash).
I forgot to photograph the sauce before we demolished most of it, so here's a photo of what was left after dinner.

1 medium sized brown onion

1 spring onion (green onion)

1 cup + 3 tbsp Greek yoghurt

¼ tsp salt

1 cube fish stock

1 tsp dried dill

Chop the onions and place in a bowl or jug you can use with your hand blender. Crumble the stock cube over the onions and add 3 tbsp Greek yoghurt. Liquidise with a hand blender. When all of the onion has been liquidised, mix with the rest of the yoghurt, salt and dried dill. Let sauce sit in the fridge for a good hour at least to get the most of the flavours.