Position an oven rack at the center of the oven, and preheat to 400 degrees F. Line 2 baking sheets with parchment.
Whisk together the flour, sugar, baking powder and salt in a large bowl. Add the cream, lemon juice and lemon zest, and stir with a wooden spoon until the mixture just forms a dough. Gather the dough into a ball, and transfer it to a flour-dusted work surface. Pat it into a 1/2-inch-thick circle. Cut out as many mini biscuits as you can with a 1-inch round cookie cutter. Gently press the scraps together, and repeat. Arrange the biscuits 1 inch apart on the prepared baking sheets. Brush them with more cream, and sprinkle with a little sugar.
Bake 1 sheet of biscuits on the center rack until they are just golden, about 10 minutes; repeat with the second sheet. While they are still warm, use the rounded side of a 1/4 teaspoon measuring spoon to make an indentation on the top of each. Transfer to a rack to cool completely.
Toss together the strawberries and jam in a small bowl, and fill each biscuit indentation with some of the mixture. Top with a small dollop of whipped cream and a mint leaf. (The shortcakes can be made and refrigerated up to 2 hours before serving.)
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