Preheat oven to 375 degrees F.

Heat olive oil in a 9 or 10 inch cast iron skillet over medium heat on the stove. When warm, add onion and cook for 6-7 minutes, until onion is translucent and softened. Add garlic and cook for another minute, until garlic is fragrant. Push to once side of pan, and add beef, salt, and black pepper. Cook, stirring and breaking beef apart into small pieces with a wooden spoon, until meat is no longer pink. (You can mix the onion in as you do this) When no longer pink, add spinach and stir into the ground beef and continuing to cook until spinach is wilted down. It will seem like a lot of spinach, but it will shrink.

Scrape mixture into a bowl and set aside. Return skillet to stovetop and bring to medium heat. Add butter, then sweet rice flour. Whisk flour into butter and cook for 2-3 minutes, until flour is a paste and no longer raw. Whisk in milk and stir continuously, cooking for 3ish minutes until sauce starts to thicken and small bubbles are forming on sides of pan, but not boiling.

Remove from heat. Whisk in sour cream, mustard, white wine vinegar, and worchestire sauce until you have a smooth sauce. Add beef mixture back to skillet and stir to completely coat all ingredients. Add 3 ounces of gruyere cheese and stir to combine. Smooth top of mixture. Then add remaining 2 ounces of cheese to the top, and then place tater tots next to each other in a circular fashion, covering the skillet with tater tots.

Bake for 20 minutes at 375 degrees F. Then increase heat to 400 degrees F, and cook for another 10-12 minutes to brown the tater tots. You'll see their crispness, and some of the cheese bubbling throughout the pan.