Preheat the oven to 375ºF.

In a small saucepan, melt the butter. Whisk in the flour and cook for 90 seconds. Slowly whisk in the vegetable broth. Bring to a boil, and cook for 2 minutes, whisking frequently. Add the tomato sauce, chili powder and cumin. Bring back to a boil, then reduce the heat and simmer for 6-8 minutes, until slightly thickened. Season to taste with salt and pepper. Spread 3/4 cup of the sauce in the bottom of a 13x9-inch baking dish.

Meanwhile, heat the olive oil in a large sauté pan. Add the onion and garlic and cook until tender. Stir in the mushrooms and cook an additional 3 minutes. Add in the artichokes and spinach and cook for 5 more minutes. Season to taste with salt and pepper. Remove the pan from the heat and stir in the ricotta, sour cream, and 1 cup of the cheese.

Place 2/3 cup of the filling down the center of each tortilla, then roll and place in the baking dish, seam side down. Pour the remaining sauce over the top, then sprinkle with the remaining 1 cup of shredded Monterey Jack.

Bake, uncovered, for 20 minutes, then turn on the broiler until the cheese is bubbling and browned. Sprinkle with fresh cilantro, if desired.