Cut off the thick stems of the spinach and discard. Clean the spinach by filling up your sink with water and soaking the spinach to loosen any sand or dirt. Drain the spinach and then repeat soaking and draining.
Blanch the spinach in a pot of boiling water until the spinach is wilted, about 1-2 minute Drain and rinse in cold water to stop the spinach from cooking further. Squeeze to remove all the moisture possible. Chop and set aside.
Heat a large skillet on med. high. Add the chopped bacon and sauté until the bacon begins to render some fat. Add the chopped onion and garlic. Sauté until onions are translucent.
Make the béchamel sauce. Melt butter in a small saucepan on med/low heat until it just starts to bubble. Add the flour and cook, stirring until smooth, about 2 minute Slowly add the milk, whisking continuously, cooking until thick.
Combine spinach, bacon and onion mix, and béchamel sauce into one pan. Add nutmeg, salt and pepper to taste. Bring to a simmer, remove from heat and serve.