I have a good one with blue cheese, but not feta. I am sure you could substitute. If you want it...
here it is:
Mashed Potatoes Florentine
8 ounces fresh baby spinach
4 bacon slices, chopped (opt.)
2 shallots, minced
3 lbs potatoes, peeled or unpeeled
2-1/2 qt water (approximately)
salt
1/2 cup milk
1/2 stick (1/4 cup) butter
Additional salt, pepper to taste
Nutmeg to taste
8 ounces crumbled blue cheese, divided
Bring the water to a boil and add salt. Add potatoes, reduce the heat to medium, and cook until the potatoes are tender, about 35 min. Drain immediately.
Slowly add the hot milk to the potatoes, stirring constantly. Mash potatoes and season with more salt, pepper, and nutmeg to taste.
Remove large stems from spinach. Saute bacon in a large skillet over medium-high heat until crisp; remove and drain bacon, reserving drippings in skillet. Add shallots to skillet, and saute until tender; remove from skillet.
Add spinach, and cook 5 minutes or until wilted. Set aside.
Combine mashed potatoes and butter in a 2-quart microwave-safe bowl. Microwave at HIGH 15 minutes, stirring once. Let stand 2 minutes. Stir in bacon, shallots, and half of crumbled blue cheese.
Serve potatoes on a bed of the spinach mixture and top with additional blue cheese if desired.