Toss sliced strawberries with 1/4 cup granulated sugar in a bowl and set aside for 30 minutes to create a syrup.

Preheat oven to 425°F (218°C) and line a baking sheet with parchment paper.

Whisk together flour, remaining 1/4 cup granulated sugar, baking powder, and salt in a large mixing bowl.

Cut cold butter into the flour mixture using a pastry blender until it resembles coarse crumbs.

Whisk the milk and egg together, then stir into the flour mixture until just combined; do not overmix.

Drop six large spoonfuls of dough onto the baking sheet and bake for 12 to 15 minutes or until golden brown.

In a separate chilled bowl, beat heavy cream, powdered sugar, and vanilla extract until stiff peaks form.

Slice the warm biscuits in half, layer the bottom with strawberries and whipped cream, then replace the top half of the biscuit.