In a large skillet over medium heat, heat the olive oil. Add the garlic and cook for 30 seconds. Add the spinach and chopped jalapeño and cook, stirring frequently, for 3 to 4 minutes, until the spinach wilts.
Remove the pan from the heat and stir the crumbled Queso Fresco into the spinach, stirring well until the cheese softens.
Taste and season with salt and pepper, as needed.
Lay four tortillas out on a clean space. Divide the spinach mixture among them, using a spoon to smooth the mixture to the edges of the tortillas.
Top each with another tortilla.
Heat a large dry cast-iron skillet over medium heat.
Using a large spatula, lift the first filled tortilla into the pan.
Cook for 2 to 3 minutes per side, until the tortilla is golden brown and the edges are slightly crisp.
Remove to a cutting board and use a large sharp knife to cut the quesadilla into quarters.
Keep warm on a serving platter while you cook the remaining quesadillas.
Serve with Ranchero® Crema Natural and salsa, if desired.