Pierogi with onion cream sauce

Someday, I will attempt to make pierogi from scratch. Until then, I like the Trader Joe's variety best but Mrs. T's is ok too!

1 box frozen potato and cheese pierogi
2 tablespoons oil, divided
1 large sweet onion, thinly sliced
1 tablespoon minced garlic
1/2 red bell pepper, thinly sliced
1/2 pound mushrooms, sliced
1/4 cup cream (fat free half and half works nicely)
1 tablespoon butter

Cook pierogi in boiling water, according to package directions.

Meanwhile, heat one tablespoon of the oil over medium heat. Add onions, garlic, peppers, and mushrooms. Saute for five minutes or until onions are soft. Add cream and butter, stirring until butter is melted. Remove from pan.

Add remaining oil to the pan, and brown pierogis according to package directions. When they are fully cooked, add onion mixture back to the pan, cover and simmer for five minutes, until sauce is heated through. Serve immediately.