Preheat oven to 300 degrees. Thinly slice the mushrooms. Mince or grate the garlic. Halve, peel, and mince the shallot. Strip the thyme leaves off the sprig, then roughly chop. Finely chop the parsley. Slice half the polenta into 1/2-inch thick slices (save the rest for another day!)

Heat 1 tablespoon olive oil in a large pan over medium-high heat. Once hot, sear the polenta for 2-3 minutes per side, until golden brown. Transfer to a baking sheet and place in the oven to keep warm.

In the same pan, heat 1 tablespoon butter over medium-high heat. Add the mushrooms to the pan and cook, tossing, 5-6 minutes, until golden brown. Season with salt and pepper and set aside.

Add 1 teaspoon oil to the same pan over medium heat. Add the shallot, thyme, and garlic to the pan and cook 2-3 minutes, until softened. Add 1/2 cup water and the stock concentrate to the pan. Bring mixture to a boil, then reduce to a simmer until reduced and thickened, 2-3 minutes. Remove pan from heat, then stir in the sour cream, mushrooms, and a pinch of salt and pepper.

Toss the arugula with 1 tablespoon balsamic vinegar and a large drizzle of olive oil. Season with salt and pepper.

Plate the polenta cakes and top with the mushroom ragu. Serve the arugula salad to the side and enjoy!