Heat a 12” skillet over medium heat, then wilt spinach in a skillet with a pinch of salt. Once wilted, remove from skillet, set aside to cool, then squeeze out excess water.
To the skillet, add butter and allow to melt, followed by onion and a pinch of salt. Sauté until translucent, about 5-7 minutes. Add in garlic, oregano and red pepper flakes and cook stirring frequently until garlic is fragrant, about 30 seconds.
Preheat oven to 350°F. Add in cream cheese and sour cream to the skillet, and stir over medium-low heat until creamy and combined, about 5 minutes.
After the cheese mixture is smooth, add in artichoke hearts, wilted spinach, 4 ounces of parmesan and 6 ounces of mozzarella, reserving remaining cheeses to top the dip before it goes into the oven. Stir until cheeses are melty and combined. Adjust seasonings to taste. Smooth the mixture, and top with remaining mozzarella and parmesan cheeses. Add to a hot oven and bake until bubbly and topping is golden brown, about 20-30 minutes.
Serve with a variety of vessels to suit any dietary preference. Enjoy!