Jam: Cook strawberries, sugar, and lemon juice in a large pot over medium-high heat, stirring occasionally, until reduced to 4 cups, about 12 minutes. Let cool completely. (Jam can be stored in refrigerator for up to 3 days.)

Biscuits: Meanwhile, preheat oven to 375 degrees with a rack in lower third and a baking sheet on rack below. Whisk together flour, baking powder, granulated sugar, and salt. Cut in butter until largest pieces are the size of peas. Mix in cream with a fork until dough starts to come together but is still crumbly. Turn out onto a work surface; knead once or twice to make smooth. Pat dough into an 8-inch round, about 3/4 inch thick. Cut into 8 wedges.

Spread 3 cups jam in bottom of a 9 1/2-inch deep-dish pie plate or skillet. Arrange dough on top in a round, then brush with cream and sprinkle with sanding sugar. Bake until bubbling and golden (if top is browning too quickly, tent with foil), about 50 minutes. Let cool before serving with remaining jam and whipped cream.