Peel the 8 large waxy potatoes and cut into roughly 1 cm cubes.
Cook the potato cubes in lightly salted water or chicken broth over medium-high heat until tender (about 10-15 minutes). Drain and set aside, keeping warm.
Cut the chicken breasts or legs into roughly 1 cm cubes.
Clean the mushrooms and cut into roughly 1 cm cubes.
Heat butter in a sauté pan over low heat. Add the chicken cubes and stir constantly for 2-3 minutes.
Add the mushroom cubes and increase heat to medium-high. Cook until the mixture begins to brown (about 3-5 minutes), then pour in 1 glass of sherry and add a pinch of salt.
Pour in 1 shot of white wine, cover the pan, and cook over high heat for 4 minutes.
Stir in the cream and season to taste with salt and pepper.
Uncover the pan and reduce the sauce over medium-high heat until it reaches a creamy consistency.
Remove from heat, add the warm potato cubes, season with 2 teaspoons of black pepper, and stir gently to combine.