I used this recipe. It only took 15 minutes to make the balsamic reduction, not 50 as stated. I mixed the garlic in directly with the mushrooms before baking as I intended to eat them immediately and wanted to avoid the pan-frying stage. Rather than coat them in oil I just sprayed the baking paper.
I served the mushrooms with salted, boiled potatoes and carrots which were also coated with the balsamic reduction and baked alongside the mushrooms.
Leftover reduction was used on brussels sprouts.