Toss berries with 2/3 cup sugar in bowl. Cover and refrigerate 3 hours. (Can be prepared 6 hours ahead.)
Preheat oven to 400 degrees. Combine flour, remaining 2 tablespoons sugar, poppy seeds, cream of tartar, baking soda and salt in bowl. Cut in butter until mixture resembles coarse meal. Add half & half; mix just until moist clumps form. Turn dough out onto floured surface; roll out into 1/2-inch thick round.
Cut out biscuits until 3-inch round cookie cutter. Transfer to heavy, large cookie sheet, spacing apart. Bake until golden brown, about 12 minutes. Cool biscuits on rack.
Using serrated knife, cut biscuits horizontally in half. Place lower halves cut side up on plates. Top with berries and dollops of whipped cream. Cover with biscuit tops. Serve, passing remaining berries separately.