This is a nice summery dish and serves well warm or cold.
1 Tablespoon Butter
1 Tablespoon Olive Oil
2 x Medium Red Onions (thinly sliced preferably with a mandolin)
2 lb New Potatoes (par boiled)
1 x Tablespoon Soft Brown Sugar
1 Tablespoon Balsamic Vinegar
Gas 4; 180C
Once, par boiled, add the potatoes to a roasting dish and spread the onions over the top.
Sprinkle over the rest of the ingredients and pop into the oven for about an hour, stirring occasionally.