Add the reserved bacon drippings or the olive oil to a heavy skillet over medium heat until fragrant, then add the mushrooms and shallots and sauté until they are golden, but not brown. Add the bacon strips, stir well and turn off the heat.
Add the warm spaghetti and blend all ingredients together thoroughly. Add the warm b?chamel sauce, pepper, parsley and salt and blend thoroughly.
Serve immediately with Parmesan.
Sauce: In a heavy non-aluminum pot, melt butter and add flour and cook on moderate heat for 2 minutes, stirring constantly with a wire whisk. Do not allow the roux to color more than blond. Add milk (no skim or low-fat) and bring to just below the boiling point. Remove from heat immediately and keep warm (180°s; F).Makes 4 Source: