Country Rhubarb Cake

Put oven rack in middle position and preheat oven to 400°F. Butter a 10-inch glass or ceramic pie plate or a 2 1/2-quart oval gratin dish and chill.

Toss rhubarb with brown sugar in a bowl until coated.

Whisk together flour, baking powder, and 1/2 cup granulated sugar in a large bowl until combined well. Blend in butter with a pastry blender or your fingertips until mixture resembles coarse meal.

Whisk together milk, whole egg, and yolk. Make a well in center of flour mixture and add milk mixture, stirring with a wooden spoon to gradually incorporate flour and form a soft, sticky dough.

Transfer half of dough to chilled pie plate and pat out over bottom and halfway up side with well-floured hands, then spoon rhubarb and any juices onto dough. Using a tablespoon, spoon remaining dough in small mounds evenly over top. Lightly beat egg white with a few drops of water, then lightly brush cake with egg wash.

Sprinkle remaining 2 tablespoons granulated sugar over top.

Bake cake until top crust is golden and rhubarb is tender, 30 to 40 minutes.

Transfer to a rack to cool, about 30 minutes.

Beat cream with confectioners sugar, whiskey, and vanilla in a bowl with an electric mixer until it forms stiff peaks.

Serve cake warm or at room temperature with whiskey cream.

Cake can be made 4 hours ahead and cooled completely, then kept, wrapped well in plastic wrap, at room temperature. Reheat if desired.