Those smarty pants over at America's Test Kitchen are at it again: these biscuits take their inspiration from the classic buttermilk variety, but they contain no buttermilk whatsoever. What's replaced that rich, tangy flavor? Sweet potatoes and vinegar.
It may seem odd, but remember that before there was commercially available baking powder, vinegar was a common baking ingredient. You won't taste the vinegar at all after they're baked, just buttery, delicious biscuits!
Sweet Potato Biscuits
Makes 16 biscuits
2 1/2 lbs sweet potatoes (4 to 5 medium)
2 tbsps cider vinegar
3 1/4 cups cake flour (You can substitute a combination of 2 1/4 cups plus 3 tablespoons all-purpose flour and 7 tablespoons cornstarch for the cake flour.)
1/4 cup packed dark brown sugar
5 tsps baking powder
1/2 tsp baking soda
1 1/2 tsps salt
8 tbsps (1 stick) unsalted butter, cut into 1/2-inch pieces and chilled; plus 2 tablespoons unsalted butter, melted
4 tbsps vegetable shortening, cut into 1/2-inch pieces
Prick potatoes all over with fork. Microwave on large plate until potatoes are very soft and surface is wet, 15 to 20 minutes, flipping every 5 minutes. (If you halve the recipe, reduce the microwave time down to 10 to 15 minutes.) Immediately slice potatoes in half to release steam. When cool enough to handle, scoop flesh into bowl and mash until smooth. (You should have 2 cups. Reserve any extra for another purpose.) Stir in vinegar and refrigerate until cool, about 15 minutes.
Adjust oven rack to middle position and heat oven to 425 degrees. Line rimmed baking sheet with parchment paper. Pulse flour, sugar, baking powder, baking soda, salt, chilled butter, and shortening in food processor until mixture resembles coarse meal. Transfer to bowl with cooled potatoes and fold with rubber spatula until incorporated.
Turn dough out onto floured surface and knead until smooth, 8 to 10 times. Pat dough into 9-inch circle, about 1 inch thick. Using 2¼-inch biscuit cutter dipped in flour, cut out biscuits and arrange on prepared baking sheet. Pat remaining dough into 1-inch-thick circle and cut out remaining biscuits.
Brush tops of biscuits with melted butter and bake until golden brown, 18 to 22 minutes. Let cool 15 minutes. Serve. (Biscuits can be stored at room temperature in an airtight container for 2 days.)