Caviar and Salmon Blini Tortes

Name: Caviar and Salmon Blini Tortes
Ingredients: 1 hard-boiled large egg, finely chopped; 2 tablespoons sour cream; 1 tablespoon finely chopped chives; 2 tablespoons buckwheat flour; 3 tablespoons all-purpose flour; 1 teaspoon sugar; 1/8 teaspoon baking soda; 1/8 teaspoon salt; 1/4 cup whole milk; 1 large egg, separated; 1/2 stick unsalted butter, melted and cooled, divided; 1/4 lb thinly sliced smoked salmon at room temperature; 2 ounces trout caviar, such as rainbow- trout caviar, or salmon roe; Garnish: sour cream; chopped chives