Peel and finely chop the onion. Heat a couple of tablespoons of extra virgin olive oil in a saucepan and fry the onion together with the sugar, over very low heat for 10 minutes. If you cover the pan, cooking will be more uniform and faster.
Add the strawberries. Blueberries, currants, blackberries, raspberries, etc. can also be used. Increase the power of the fire and, when it reaches the boiling point, add the Port wine. Let it reduce.
Add the broth and bring it back to a boil.
Cook for 10 minutes over medium heat before crushing and passing through a sieve.
Taste the point of flavour and adjust with a pinch of salt and black pepper if you consider it necessary.
Add the butter and bbq sauce and stir until melted.