Double-Lemon Thumbprint Scones

Position rack in center of oven and preheat to 425°F. Line large heavy-duty rimmed baking sheet with parchment paper. Finely grate enough peel from lemons to measure 6 teaspoons; set grated peel aside. Squeeze enough juice from 1 lemon to measure 1 tablespoon (seal remaining lemons in plastic wrap and reserve for another use). Whisk flour and 1/2 cup sugar in medium bowl to blend. Add 1 1/4 cups chilled whipping cream, 1 tablespoon lemon juice, and 4 teaspoons finely grated lemon peel; stir gently to combine.
Gather dough together and turn out onto lightly floured work surface; knead briefly, 4 to 5 turns. Pat or roll out dough to 1-inch-thick round. Using 2 1/2-to 2 3/4-inch-diameter cookie cutter or biscuit cutter dipped in flour, cut out rounds. Reroll dough scraps and flatten to 1-inch thickness; cut out additional rounds. Transfer scones to prepared rimmed baking sheet, spacing scones about 1 inch apart. Using thumb, push down center of each scone to make deep indentation. Spoon about 1/2 teaspoon preserves into indentation of each scone.
Whisk remaining 2 tablespoons sugar, 2 tablespoons heavy whipping cream, and 2 teaspoons finely grated lemon peel in small bowl to blend. Brush top of scones generously with lemon glaze. Bake scones until golden and cake tester inserted horizontally into center of scone comes out clean, 18 to 20 minutes. Transfer thumbprint scones to rack and cool slightly. Serve scones warm or at room temperature.