Step 1Squeeze any excess water from the thawed spinach and place the spinach in a large mixing bowl.
Step 2Stir in the bread crumbs, Swiss cheese, Parmesan cheese, onion, garlic, eggs and butter until thoroughly combined.
Step 3Cover and chill the mixture until it is firm enough to form into balls.
Step 4Heat the oven to 350 degrees. Line 2 cookie sheets with foil, and lightly oil the foil.
Step 5With a spoon, scoop enough of the spinach mixture to form balls approximately 1 inch in diameter. Roll the mixture into balls and place on the foil-lined cookie sheet, spacing them 1 to 2 inches apart. Repeat until all the mixture is used.
Step 6Bake the sheets, one at a time, until lightly browned and firm, 15 to 20 minutes.
Step 7Cool slightly before serving.