Make the filling: Combine the grapes, all-purpose flour, sugar, vanilla and almond extracts, lemon juice and salt in a large bowl. Toss to coat the grapes.
Preheat the oven to 375 degrees F. Make the topping: Whisk the all-purpose flour, almond flour, sugar, baking powder and salt in a medium bowl. Work the butter into the flour mixture with your fingers until it looks like coarse meal with pea-size bits of butter. Lightly beat the egg and heavy cream in a small bowl; add to the flour mixture and stir a few times until a sticky dough forms.
Spread the filling in an 8-inch square baking dish. Drop heaping tablespoonfuls of the biscuit topping over the grapes, leaving a small space between each spoonful. Sprinkle the topping with sugar and the almonds.
Bake until the biscuits are golden brown and puffy and the filling is bubbling, 40 to 50 minutes. Transfer to a rack and let cool at least 30 minutes before serving.
Photograph by David Malosh