Strawberry Shortcake

2 1/2 lb strawberries, trimmed and quartered (7 1/2 cups)
1/3 to 1/2 cup granulated sugar, or to taste
1 cup chilled heavy cream
1/4 cup sour cream
1 1/2 to 2 tablespoons confectioners sugar
1/2 teaspoon vanilla
6 buttermilk biscuits

Special equipment: a potato masher

Toss strawberries with granulated sugar in a large bowl and let stand 5 minutes. Gently press strawberries with potato masher to help release their juices, being careful not to crush them to a pulp. Let stand at room temperature, stirring occasionally, 45 minutes to 1 hour.
Beat together heavy cream, sour cream, confectioners sugar (to taste), and vanilla in a bowl with an electric mixer at medium-high speed until it holds a soft shape(not stiff).
Split biscuits horizontally with a fork and arrange 2 halves, split sides up, on each of 6 plates. Top with strawberries and juices, then with whipped cream.