Rinse collard greens. Trim and discard thick stems from bottom of greens and coarsely chop.
Cook bacon, in batches, in a 8 quart stock pot over medium heat, 10 to 12 minutes or until crisp. Remove bacon with a slotted spoon and drain on paper towels, reserving drippings in stock pot. Reserve 1/4 cup bacon.
Add butter and onions to hot drippings in skillet. Saute onion 8 minutes or until tender. Add collards, in batches, and cook stirring occasionally, 5 minutes or until wilted. Stir in chicken broth, next 3 ingredients and remaining bacon.
Bring to a boil. Reduce heat to low, and cook, stirring occasionally, 15 minutes or to desired degree of tenderness. Drain collards, reserving 1 cup liquid.
Stir in Bechamel Sauce. Stir in reserved cooking liquid, 1/4 cup at a time to desired consistency. Sprinkle with reserved bacon.
Bechamel Sauce: Melt butter in heavy saucepan over low heat, add shallots and garlic and saute l minute. Whisk in flour until smooth. Cook 1 minute, whisking constantly. Increase heat to medium, gradually whisk in milk. Cook over medium heat, whisking constantly, 5 to 7 minutes or until mixture is thickened and bubbly. Stir in salt, pepper and nutmeg.