Buckwheat Waffles with Orange Maple Syrup

Name: Buckwheat Waffles with Orange Maple Syrup
Ingredients: 1 teaspoon finely grated orange zest, plus 1 cup fresh orange juice (from 2 to 3 oranges); 1/2 cup amber maple syrup; Pinch of kosher salt; 6 tablespoons cold unsalted butter, cut into pieces; 3/4 cup all-purpose flour; 1/2 cup buckwheat flour; 1/3 cup cornstarch; 3 tablespoons sugar; 1 1/2 teaspoons baking powder; 1/2 teaspoon ground cardamom; 1/2 teaspoon kosher salt; 1 1/4 cups milk; 1/4 cup vegetable oil; 2 large eggs, separated, at room temperature; 1 teaspoon vanilla bean paste; Cooking spray; 1 cup sour cream; 1/2 teaspoon vanilla bean paste; 2 oranges, peels cut off, sliced crosswise into rounds and halved