-
Preheat oven to 425°F with rack in middle.
-
Lightly butter a baking sheet.
-
Whisk together flour, baking powder, and salt. Stir in cream just until a dough forms. Gather dough into a ball and gently knead together once or twice on a lightly floured surface.
-
Roll or pat out dough into a 6-inch square (about 1/2 inch thick). Trim edges with a floured knife and cut into 4 squares. Brush tops with cream and sprinkle with turbinado sugar. Bake on baking sheet until golden, 15 to 20 minutes, then transfer biscuits to a rack to cool.
-
While biscuits bake, cook rhubarb with granulated sugar and butter in a medium saucepan over medium heat, stirring occasionally, until fruit is very tender and falling apart, about 10 minutes.
-
Stir together Sherry and cornstarch, then add to rhubarb mixture and simmer, stirring, until mixture is slightly thickened, 1 to 2 minutes.
-
Split biscuits, then sandwich rhubarb and whipped cream inside them.
