Portobello Burgers with Roasted Onions

A little while ago I promised you some roasted portobello burgers once it got cooler. It is only slightly cooler, but I couldn't resist because this is probably one of our favorite meatless burger alternatives.

Portobello is a very flavorful, meaty mushroom which makes it a good base for a burger. Its texture is firm, so it can withstand and be much improved by potent marinades that you would for instance use to marinade a steak, with ingredients like garlic, balsamic vinegar, rosemary, among others. In this recipe I used a balsamic vinegar and olive oil mixed with a few spices, but as always, feel free to experiment with your own seasonings.

The roasted onions go really well with the portobello burgers. I was going to top these off with some mozzarella cheese and a few toppings like tomato or pickles, but Tony - who had been patiently waiting while I was photographing these - finally came in the room seemingly hungry. So I quickly finished up before these got cold and we just gulped them down as they were, with a little ketchup. Nothing else was needed.

Portobello Burgers with Roasted Onions
(Serves 2)

You will need:
2 large portobello mushrooms
1/3 cup (79 ml) balsamic vinegar
2 tbsp olive oil
2 garlic cloves, crushed
1 tbsp chopped fresh parsley
1/4 tsp salt
1/8 tsp black pepper
1/8 tsp paprika
A quarter of red onion, sliced into circles
Burger toppings and buns

Directions:
1. Carefully trim off the stems at the base of the mushrooms. Discard the stems or use them elsewhere, leaving only the caps. Carefully rinse the caps under a trickle of water, gently rubbing off any dirt with your fingers so as not to rub off the skin.
2. In a measuring cup, combine balsamic vinegar, olive oil, garlic, parsley, salt, pepper and paprika. Pour a bit of the marinade over the gills of the mushrooms. Place the mushrooms gill side down together with the onion slices in a flat-bottomed dish and pour the rest of the marinade over them. Cover and refrigerate for 40 minutes to 1 hour.
3. Preheat the oven to 400ºF/205ºC. Line a baking sheet with foil and grease with a bit of olive oil. Place the mushrooms, gill side down, along with the onions on the baking sheet and cover with foil loosely. Bake, 30-40 minutes, until the mushrooms are tender. Serve on buns with the onions, along with your preferred burger toppings.