Cook ravioli according to package instructions. Set aside, covered.

Heat olive oil and butter in a large skillet, preferably with high sides. Add onion and sauté over low-medium heat for 30 minutes, until very soft and lightly golden, stirring occasionally. Add mushrooms and continue sautéing for 10 minutes, stirring often, until wilted. If necessary, spray vegetables with cooking spray midway.

Add flour and mix until all vegetables are coated. Add milk, cooking cream, and seasonings and cook over low heat for 10 minutes, or until mixture is thickened. Stir often. Taste and adjust seasoning if necessary. Stir together with cooked ravioli. Garnish, if desired.