Place thawed spinach between several layers of paper towels. Roll up like a jelly roll and press firmly. Unroll, fluff with a fork, and set aside.

Fill a large pot with lightly salted water and bring to a boil. Cook fettuccine until tender yet firm to the bite (about 8 minutes), drain, and reserve 1/2 cup pasta water.

Cut cream cheese into chunks and place in a non-stick skillet over medium-low heat. Add cream and stir until cream cheese melts.

Add garlic, Parmesan, and mozzarella. Stir until cheeses melt and sauce becomes bubbly.

Add sour cream and mayonnaise. Mix well to blend.

Add spinach and artichokes, stirring until heated through (about 2 minutes). Optionally, add pasta water (1 tablespoon at a time) to loosen sauce, if desired.