Brown chicken in hot butter; remove chicken. Add garlic and onion to butter; cook 2 to 3 minutes. Remove from heat and stir in tomato paste and flour until smooth. Add chicken stock a little at a time, stirring until smooth. Then blend in sherry, and stir over low heat until mixture comes to a boil. Add the browned chicken, almonds, salt, pepper and tarragon. Cover and cook slowly for 45 to 50 minutes. Remove from heat and arrange chicken in a shallow casserole. Stir sour cream into liquid in which the chicken was cooked. Pour sauce over chicken. Sprinkle with cheese. Garnish with skinned tomato and brown under broiler.