Wipe the chicken fillets dry with paper towels, cut into thin strips and toss with a teaspoon of salt and a quarter teaspoon of pepper.

Cut the mushrooms into halves, quarters or slices, depending on how large they are.

Peel and thinly slice the onion.

Rinse and drain the spinach and roughly chop.

Peel the garlic, grate and stir into the sour cream.

Set the stove to medium-high and melt the butter in a thick-bottomed frying pan.

Spread the chicken strips in the hot butter, allow the undersides to brown a bit before stirring. Cook for a few minutes.

Add the mushrooms to the chicken. Sprinkle in a bit of salt and pepper. Cook, stirring, until the mushrooms start to brown.

Add the onion slices. Continue cooking, stirring, for another minute.

Throw in the spinach, sprinkle in a bit more salt and pepper, and cook until wilted and the mixture is almost dry.

Pour in the sour cream and stir. When the sauce is bubbly, turn off the heat.

Taste the sauce, add more salt and pepper, as needed, before serving.