Melt ½ tablespoon of butter in a pan over medium heat. Add chicken thighs and cook for about 3-5 minutes, seasoning with sea salt and black pepper. Flip and cook until both sides are golden brown. Transfer to a bowl and set aside.

In the same pan, add the remaining butter. Once melted, sprinkle in the flour and toast lightly until golden. Gradually add milk in quarter increments, mixing until the sauce is smooth and creamy.

Return the cooked chicken to the pan with the sauce and stir until well combined. Adjust seasoning if needed.

Toast one tortilla in a clean pan over low heat. Sprinkle ⅕ cup each of cheddar and mozzarella cheese onto it. Spoon ¼ of the creamy chicken mixture on top, followed by another ⅕ cup each of cheeses. Place another tortilla on top.

Cook until the bottom tortilla’s edges turn light brown. Carefully flip and toast the other side for another 3 minutes until crispy.

Transfer the quesadilla onto a cutting board and slice it into four parts. Repeat with remaining tortillas and filling.