Irish Tarte Tatin

2 pounds rhubarb, trimmed and cut into 1-inch pieces
1 1/4 cups sugar, plus additional, if needed

For the scone dough
2 1/2 cups all-purpose flour
2 tablespoons superfine sugar
1 heaping teaspoon baking powder
Pinch salt
4 tablespoons (1.2 stick) unsweetened butter, cut into medium dice
1 egg
3/4 cup milk, plus more, if needed
1 egg, beaten, for the wash
Sugar, for sprinkling

Preheat the oven to 450 degrees F. Put the rhubarb into a pie dish or a sauté pan (see head note) and sprinkle it with the sugar. Taste the rhubarb and add more sugar, if needed. Into a bowl sift all the dry ingredients for the scone dough. Rub the butter into the flour until the mixture resembles coarse bread crumbs. (Not hard to do by hand, but I tend to use my free-standing mixer.) Whisk the egg with the milk. Make a well in the center of the dry ingredients, pour in the liquid all at once, and mix to a soft dough. Turn out onto a floured board and roll into a 9-inch round (or the size of the dish you’re using) about 1 inch thick. Place this fat disc on top of the rhubarb and tuck in the edges neatly. Brush with a little of the beaten egg and sprinkle generously with sugar. Bake in the preheated oven for 15 minutes, then reduce the temperature to 350 degrees F for about 30 minutes more, or until the top is crusty and golden and the rhubarb soft and juicy. Remove the pan from the oven and allow to sit for a few minutes. Put a warm plate over the top of the pan and turn it upside-down so that the pie comes out on the plate.