1. Combine first 6 ingredients.
2. Weigh or lightly spoon flour into a dry measuring cup; level. Combine flour and next 3 ingredients (through 1/4 teaspoon pepper) in a medium bowl. Combine buttermilk and egg yolk; add milk mixture to flour mixture, stirring with a whisk just until moist.
3. Place egg white in a bowl; beat with a mixer at high speed until medium peaks form. Fold one-fourth of egg white into buttermilk mixture. Gently fold in remaining egg white.
4. Heat a large skillet over medium-high heat. Lightly coat pan with cooking spray. Spoon about 1 tablespoon batter per pancake into pan, spreading slightly. Cook 1 minute or until tops are covered with bubbles and edges begin to set. Turn and cook 1 minute. Repeat with remaining batter for a total of 16 pancakes. Top each pancake with 1/4 teaspoon crème fraîche and 1 1/2 teaspoons tomato relish. Serve immediately.