Saute the chicken on both sides in butter, remove from the skillet. Add the onion and garlic, cook and stir for 2 to 3 minutes. Add tomato paste and flour to the skillet, stir until blended and smooth. Gradually add the chicken stock and sherry, cook and stir until smooth and slightly thickened. Return the chicken to the skillet. Add the almonds, tarragon, salt, and pepper.

Cover and simmer over low heat for 30 minutes on until tender. Arrange the chicken in a shallow baking dish. Stir the sour cream into the sauce and pour over the chicken. Sprinkle with grated cheese and brown under broiler.