Trader Joe's or Bust - Mushrooms and Polenta

Robin and I have decided that we are going to try to shop exclusively (or as close as we can come) at Trader Joe's and farmer's markets. I think that this is totally possible and will save us a TON of money in the long run. Last night I made my first exclusively TJ's meal since we made our pact: Polenta topped with mushrooms.

2 packs sliced Crimini mushrooms
2 leeks (already trimmed and cleaned at TJs - yeah!), chopped
2 cloves garlic, minced
3 tbsp butter
2 tbsp olive oil, separated
2 green onions, chopped
1 tbsp parsley, chopped
1 tbsp arrowroot powder
1 cup water
1 tsp dried thyme
1/4 cup Sherry wine
1 tube prepared polenta
Parmesan cheese, to taste
salt and pepper

Heat butter and oil in a large saucepan over medium-low heat. Add leeks and garlic and saute for about 10 minutes until soft. Add salt and pepper to taste.

Add mushrooms and sherry and saute for 5 minutes. Add water and cover. Cook, stirring occasionally, 10 minutes. Uncover and let simmer over medium-low heat until the sauce reduces a bit.

While the sauce is reducing, slice polenta into 1/4 in. discs. Add 1 tbsp olive oil to a large nonstick skillet. Heat on medium heat. When pan is hot, add polenta and fry for 5 minutes on each side. Remove from pan and let cool on paper towels.

Take 1 tsp arrowroot and dissolve in 2 tbsp water. Add to mushroom sauce and let cook until thickened slightly, stirring occasionally. For a thicker sauce, add more arrowroot, but always dissolve in water. Add green onions and parsley. Stir and remove from heat.

Place polenta on a plate and cover with mushroom sauce. Top with Parmesan cheese.