- In bowl, mash together cheese, egg yolks and garlic.
- Mix in onions, spinach, parsley, mint and pepper.
- Butterfly chicken in half almost all the way through and lay flat.
- Spread feta mixture evenly on 1 half of each breast; fold breast back over to enclose.
- Place 1 sheet of phyllo on work surface, keeping remainder covered with a damp towel to prevent drying out.
- Brush lightly with some of the butter; top with second sheet and brush lightly with butter. Repeat with two more sheets for a total of four
- Center 1 breast on phyllo about 2 inches from the short edge; fold long sides over chicken and roll up.
- Repeat with remaining chicken.
- Place in lightly greased baking dish; brush with remaining butter.
- If making ahead, cover and refrigerate for up to 8 hours.
- Bake in 350 degree F oven until crisp and golden, about 45 minutes.