2 1/2 c. sifted all purpose flour
1/2 c. (1 stick) chilled unsalted butter, diced
1/2 c. sugar
2 tbsp. Citrus Sugar
1 tbsp. + 1 tsp. baking powder
1/2 tsp. cream of tartar
1/4 tsp. salt
3/4 c. chilled whipping cream

Position rack in center of oven and preheat to 375 degrees. Line large cookie sheet with parchment paper. Generously butter parchment.

Steel Knife; Place first 7 ingredients in work bowl. Process until mixture resembles coarse meal. Remove cover and pour cream evenly over mixture. Using on/off turns, process just until dough forms moist clumps.

Transfer dough to lightly floured work surface. Knead gently just until dough holds together. Pat out to thickness of 1". Cut out additional rounds. Transfer biscuits to prepared cookie sheet, spacing 3" apart. Bake until light brown, about 18 minutes (biscuits will spread). Transfer to rack. Cool to just warm, about 15 minutes. (Shortcakes can be prepared 3 hours ahead. To re-warm in microwave, place 3 biscuits on large paper plate. Cook uncovered on Medium about 1 minute. Repeat with remaining biscuits.)

CITRUS SUGAR:

2 oranges
2 lemons
1 c. sugar

Using vegetable peeler, remove peel (orange and yellow parts only) in strips from oranges and lemons.

Steel Knife: Process peel and sugar until finely minced, about 1 1/2 minutes. Transfer sugar to small bowl or jar. (Can be prepared up to 2 weeks ahead. Cover and refrigerate.)

Makes about 1 cup.