Tarragon Shallot Egg Salad Sandwich

Name: Tarragon Shallot Egg Salad Sandwich
Ingredients: 8 large eggs; 1⁄2 cup sour cream; 3 tablespoons finely chopped shallots (or can substitute white, yellow or red onion); 1 1⁄2 tablespoons finely chopped fresh tarragon (to taste) or 1 teaspoon dried tarragon (to taste); 2 teaspoons white wine vinegar or 2 teaspoons tarragon vinegar; 1⁄4 teaspoon salt (to taste); 1⁄4 teaspoon black pepper (to taste); 8 slices whole grain bread or 4 kaiser rolls or 4 croissants; baby spinach leaves (optional) or romaine lettuce (optional); sliced tomatoes (optional)