Celeriac and Potato Roesti

5 Tbsp. butter

1 Lb potatoes

1 Lb celeriac

2 tsp lemon zest

2 Tbs minced celery leaves

¾ tsp. salt

¼ tsp. black pepper

Melt butter in 10-inch nonstick or well-seasoned cast-iron skillet over medium heat.  Shred & pat dry potatoes and celeriac.  Mix shredded potatoes and celeriac with salt and pepper. Mix in lemon zest and celery leaves. Spread vegetable mixture evenly in skillet; press with spatula to form compact cake. Cook until bottom crust is golden brown, pressing on potatoes occasionally with spatula, about 15 minutes.  Shake skillet or use spatula to loosen roesti. Place large plate or platter over skillet and carefully invert. Slide roesti back into skillet and cook until bottom is golden brown, 10 to 15 minutes longer. Serve immediately.  From Cook’s Illustrated.