Preheat oven to 375 degrees and spray or butter a 2-qt casserole dish and set aside.
Place your largest skillet over medium-high heat and melt 2 Tbsp butter. Add mushrooms and ½ tsp salt and cook, stirring occasionally, for 10–12 minutes until mushrooms release their moisture and the liquid cooks off. The mushrooms will begin to brown a bit on the edges. Transfer to a plate and set aside.
Return skillet to heat and add remaining 2 Tbsp butter. Add diced onion, salt, pepper and dried thyme leaves, and cook for 3–4 minutes, stirring occasionally until onions are soft and translucent. Add garlic and cook for 1 additional minute.
Pour in wine and cook until reduced by half, and then add broth and orzo and stir to combine. Bring liquid to a boil then reduce heat to medium-low and simmer for 6 minutes, stirring occasionally.
Remove from heat then add cream and Monterey jack cheese. Stir until cheese is melted then add in cooked mushrooms and any liquid that has accumulated. Season to taste with salt and pepper and transfer mixture into prepared casserole dish.
Sprinkle top with breadcrumbs and Parmesan and bake 25–30 minutes or until golden brown on top and bubbly on the sides. Allow casserole to rest for 5–10 minutes before serving.
Pinot Grigio and Sauvignon Blanc are two of the best dry white wines for cooking!