Peel and cut potatoes into wedges. Bring salted water to a boil, add potatoes, and cook for 8-10 min until partially tender. Drain well.
Cut horizontally into the thicker side of each chicken breast, fold open like a book, and pound to about 5 mm thickness.
Peel apples, remove cores, and cut into slices.
Heat 1 tablespoon clarified butter in a frying pan over medium heat. Add drained potatoes and fry for 5 min until golden and cooked through. Season with salt and pepper. Transfer to a plate.
Pat chicken breasts dry and season both sides with salt and pepper. Heat remaining 1 tablespoon clarified butter in a larger frying pan over medium-high heat. Fry chicken for 2 min per side until golden. Remove to a plate.
In the same pan over medium heat, add onions and cook for about 2 min until softened. Add apple slices and 2 tablespoon dried sage leaves. Pour in 120 ml white wine and 160 ml cream. Stir in 1 teaspoon instant chicken broth.
Return chicken to pan and simmer for 2-3 min. Check that chicken has reached 74°C (165°F) in the thickest part.
Place cooked potatoes and schnitzel on 2 plates. Stir sauce thickener into sauce until desired thickness is reached, then pour over schnitzel.