In a large saucepan at medium heat, melt the butter until the foam subsides, add the flour and cook to make roux. Cook the roux at low heat for about two minutes until it is tight and smooth with no butter weeping out of it. If you burn the roux, start over.
Slowly add half and half, about a cup at a time, stirring constantly to incorporate and avoid roux lumps. Allow the sauce to simmer, stirring frequently with a whisk, rubber spatula or wooden spoon until the sauce becomes very thick like mayonnaise. Remove from the stove, and allow it to cool down to room temperature.
Thaw and Squeeze ALL the liquid/juice from the Spinach. Stir spinach into sauce, add the remaining ingredients, stir.
Place the Spinach Dip into a microwave safe bowl, top it with cheddar cheese and wrap it with plastic wrap. Microwave it until the cheese melts and the dip is hot in the center. Unwrap and place on a serving platter. Top with chopped bacon bits, sour cream and diced red onions. Serve with assorted tortilla chips.