Preheat the oven to 350F and brush a 9"x13" baking pan liberally with Garlic EVOO.
In a large sauté pan over medium-high heat, put 1 tablespoon of olive oil. Add the diced onion and sauté until translucent. Add the greens and sauté until cooked down, about 3 additional minutes. Add the feta and ricotta to the greens and mix thoroughly. In a small cup, mix 1 teaspoon cornstarch with 2 tablespoons of water. Add to the greens. Continue cooking over medium-high heat until the mixture thickens. Season with salt and fresh-ground pepper to taste. Allow the mixture to cool until just barely warm.
Take the thawed phyllo out of the refrigerator. Unroll the sheets and cover with a clean, barely dampened towel.
Liberally brush or spray three phyllo sheets with olive oil and layer one on top of another, lining the bottom and part way up the sides of the baking pan. Add 1/3 of the spinach mixture and spread evenly over the phyllo. Continue brushing each sheet with olive oil and layering three sheets at a time followed by two more layers of spinach and ending with three sheets of phyllo on top.
Bake for 35-40 minutes until the top is deep golden brown and crisp. Allow to cool slightly and cut into squares.
This recipe uses Frescolio's Garlic Infused EVOO. You could also try it with either of the following EVOOs for a different taste: