Heat oven to 375 degrees Fahrenheit.
Mince 2 cloves of garlic and slice the bottom portion of 4 green onions (feel free to sub ½ an onion or 1 shallot if you prefer). Chop the top portion and reserve for garnish.
Trim the tough woody bottoms from ½ lb. of asparagus and discard. Cut the remaining portion of asparagus into slices.
Chop 2 packed cups of fresh spinach.
Dice ½ lb. of pre-cooked ham into small chunks, such as ham steak or leftover roasted holiday ham.
Grate 1 cup of sharp cheddar cheese (or cheese of choice).
Heat a 10 inch cast iron skillet to medium-high. Add 1 Tbsp. olive oil. Once the olive oil is heated, add the diced ham. Sauté for 4-5 minutes, stirring occasionally. Remove the ham from the skillet and set aside. Feel free to drain any extra fat if you like. Add 1 Tbsp. of olive oil to the skillet, along with 2 cups of chopped asparagus and ⅛ tsp. each kosher salt and pepper. Sauté for 4-5 minutes, stirring occasionally. Add the minced garlic and green onions. Sauté for an additional 1-2 minutes, stirring often.Remove the skillet from the heat. The egg mixture may be prepared while the ham and asparagus are sauteed in the skillet. Crack 10 eggs into a large mixing bowl. Add ⅓ cup heavy whipping cream, along with ⅛ tsp. each kosher salt and pepper. Add the 2 packed cups of chopped spinach and 1 cup of grated cheese. Stir all of these ingredients together until combined. Add the diced ham back to the skillet along with the asparagus. Arrange the ingredients evenly in the skillet. Pour the egg mixture over the top and shake the pan a bit, so that the eggs cover all of the ingredients and coat them evenly.
Place the skillet in the oven and bake for 24-25 minutes. The edges will become slightly golden brown when finished and the center should no longer be jiggly if you shake the pan. Once all of the eggs in the middle have set, it's time to remove it from the oven.
Allow the frittata to cool for 5 minutes before serving. After 5 minutes, run a knife along the edges of the skillet to loosen it. Cut the frittata into slices and serve.
To Serve: Garnish with the sliced green onions.