Preheat oven to 350 degrees.  Cook the spinach as directed, drain and dry the spinach.   In a medium bowl mix the spinach, cheeses, and egg until well blended.  Split the muffins in half, spread each half with butter and sprinkle with garlic salt.  Spread spinach mixture on each half, top with Parmesan cheese.  Bake for 10 minutes, then put under the broiler to brown and get hot and bubbly (watch carefully).  Cut each muffin half into 4 pieces to serve.