Step 1

Preheat oven to 425 degrees F. Grease a 9- x 13-inch baking dish.

Step 2

In a large skillet over medium heat, melt 6 tablespoons butter. Sprinkle chicken with salt and pepper, then add to skillet and saute about 5 minutes, or until no longer pink. Transfer to platter; keep warm.

Step 3

Whisk mustard into skillet drippings. Add tarragon and reduce slightly. Whisk in cream and milk, blending thoroughly. Reduce heat to low and simmer until sauce is slightly thickened. Add peas, return chicken to skillet, and toss to coat completely.

Step 4

In a small microwavable bowl, melt remaining butter in microwave.

Step 5

In the baking dish, lay 1 phyllo sheet on bottom, patting to fit sides. Brush with butter. Add 4 more sheets of phyllo, brushing with butter between each layer. Place chicken mixture over phyllo, then place 5 more phyllo sheets over chicken, brushing with butter between each layer. Trim excess phyllo to within 1-inch of edge of baking dish. Tuck edges neatly under and brush top with butter.

Step 6

Bake 15 minutes, or until heated through and top is crispy and golden.