Upside-Down Mushroom, Onion Tart

Upside-Down Mushroom, Onion Tart

by | Apr 19, 2016

Upside-Down Mushroom, Onion TartIngredients4 large brown onions, halved, thinly sliced50g butter1 tbs olive oil2 tsp brown sugar200g Swiss brown mushrooms, thinly sliced100g shiitake mushrooms, trimmed2 tbs thyme leaves2 tbs balsamic vinegar1 sheet ready-rolled frozen...