Italian sausages and peppers over polenta

I've been contemplating dinner with sausage and peppers over polenta for a couple of days. I've had a three-pack of peppers in the fridge that needed to be cooked, and I bought Italian sausage a couple of days ago... so, here's the invention that led to a delicious supper:

Italian sausages and peppers

Note: This recipe would probably serve four handily. I made far more sausage than we needed for the two of us, just so I could get it all cooked. Rob and I ended up eating 3 sausages in one sitting + about 1/3 cup (dry) polenta + a small bunch of kale.

8-9 Italian sausages, hot or mild
1 large yellow onion, sliced thinly in half moons
12 oz dark beer (New Belgium 1554 is tasty)
2 Tbsp stone ground yellow mustard
1/4 tsp each cumin and chili powder
1/2 tsp rosemary
salt and pepper to taste
1 each red, orange and yellow bell pepper
4-6 oz. baby portabello mushrooms
15.5 oz can fire-roasted diced tomatoes, drained, liquid reserved

Heat a deep 12-inch skillet over medium heat. Heat about 1 Tbsp olive oil. Add the sausages in a single layer, and brown on one side. Flip the sausages. Toss the onions on top of the sausages and pour in about 10 oz beer. Simmer about 10 minutes, or until sausages are done.

Remove sausages from the pan and set aside. Turn up the heat, add the mustard and spices, and (mostly) caramelize the onions. If you run out of liquid, use some of the reserved beer or tomato juice. When onions are nearly caramelized, add peppers, mushrooms and tomatoes. Simmer until peppers are tender, stirring occasionally. Nestle the sausages on top of the vegetables, cover. Turn the heat to low.

Meanwhile, cook polenta according to package directions, and finish with a handful of parmesan and a pat of butter. (I use Bob's Red Mill polenta.) I also cooked some kale.

Serve with a scoop of polenta, a couple of sausages, a pile of kale and a good scoop of the pepper mixture. Garnish with more parmesan, if desired. Delicious with a dark beer. =)