Step 1Combine flour, baking powder, salt, sugar and zest in food processor. Scatter butter over flour. Pulse until mixture resembles coarse meal. Add buttermilk. Pulse just until mixture clumps together; do not over-process.
Step 2Transfer dough to floured board, gather dough together with your hands and knead it, folding and pressing it back on itself until it holds together and is smooth, about 15 seconds. Pat or roll dough until uniformly 3/4 inch thick. Use 2 1/4-inch cutter to make 8 rounds. Transfer to greased baking sheet in single layer with 1-inch spacing. (Can be made ahead and refrigerated up to 8 hours.)
Step 1Wipe out work bowl of food processor with paper towels. Combine flour, sugar, butter, cinnamon and salt to taste in bowl. Pulse until crumbled. Set aside.
Step 1Whisk egg with salt to form glaze. Brush glaze on top of biscuits. Top each with 1 tablespoon Streusel, spreading evenly.
Step 2Bake at 400 degrees until lightly browned, about 15 to 18 minutes. (Can be baked several hours ahead and kept at room temperature. Reheat, uncovered, in 300-degree oven 10 minutes or in microwave oven at 50% power 15 to 20 seconds.)
Step 3To serve, carefully split warm biscuits. Place bottom half in center of each of 8 dessert plates. Spoon some strawberries on and around biscuit, dividing evenly. Top with Streusel half. Put 2 strawberry slices on top of each. Garnish each plate with fanned strawberry. Top with dollop of soft whipped cream. Serve immediately.