Start by generously seasoning the chicken thighs with kosher salt and freshly ground black pepper. In a large skillet, melt 1 tablespoon of unsalted butter over medium-high heat. Add the chicken and cook for 3-4 minutes per side until golden brown, then transfer to a plate and set aside.

In the same skillet, add another tablespoon of butter and allow it to melt over medium heat. Add the halved cremini mushrooms and diced shallots, sauté for about 3-4 minutes until soft and slightly caramelized. Stir in the minced garlic and fresh thyme, cooking for an additional minute until fragrant.

Sprinkle the flour evenly over the mushroom mixture, stirring constantly for about 1 minute to cook off the raw flour taste. Gradually pour in the chicken stock while scraping up any browned bits from the skillet. Add Dijon mustard, then bring to a gentle simmer, allowing it to thicken slightly.

Stir in the orzo pasta, mixing well to coat. Return the browned chicken to the skillet and cover with a lid. Cook for 8-10 minutes, stirring occasionally, until the orzo is al dente and the chicken is cooked through.

Once the orzo is tender, add baby spinach to the skillet, cooking a few minutes until wilted. Stir in the heavy cream and Parmesan cheese, mixing until the sauce is creamy and smooth. Remove from heat and garnish with chopped parsley before serving.