Preheat the oven to 450 degrees F.
Trim the rhubarb, wipe with a damp cloth and cut into pieces about 1-inch in length. Put into the base of a tin or saute pan, sprinkle with the sugar. We put the stainless steel saute pan on a low heat at this point while we make the dough.
Sieve all the dry ingredients into a bowl. Cut the butter into cubes and rub into the flour until the mixture resembles coarse bread crumbs. Whisk the egg with the milk. Make a well in the centre 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 about 1-inch thick. Place this round on top of the rhubarb and tuck in the edges neatly. Brush with a little egg wash and sprinkle with granulated sugar.
Bake at 450 degrees for 15 minutes then, reduce the temperature to 350 degrees for another 30 minutes, or until the top is crusty and golden and the rhubarb soft and juicy.
Remove from the oven and allow to sit for a few minutes. Put a warm plate over the top of the saute pan, turn upside down onto the plate being careful of the hot juices. Serve warm with soft brown sugar and whipped cream.
Use a 9 x 2-inch round pan. We use a heavy stainless steel saute pan, which works very well if you don't have a suitable pan. Parcook the rhubarb slightly first.