Cook spinach by boiling or in microwave. Drain well and squeeze out as much moisture as possible. Chop fine, using food processor of food grinder.
Cook bacon in skillet until crisp. Remove and drain. Crumble and reserve. In about 2 T of the bacon fat, saute garlic and onion over medium heat. When onion is limp, add spinach. Lower heat. Season with salt and peppers; stir well as moisture evaporates from spinach, about 1 minute. Remove from heat.
In a separate large skillet, melt butter over medium heat. Sprinkle in flour, stirring constantly until smooth. Graduallly stir in half-and-half or milk and cook until smooth and bubbly. Stir in spinach mixture and heat through. Remove from heat, stir in reserved bits of bacon, and serve.