Put the flour, icing sugar and salt in the bowl of a food processor and pulse a couple of times to combine

Scatter the pieces of butter over the dry ingredients and pulse until the butter is cut in coarsely - you'll have pieces the size of oatmeal flakes and pea-size pieces and that's just fine

Stir the egg, just to break it up, and add it a little at a time, pulsing after each addition

When the egg is in, process in long pulses - about 10 seconds each - until the dough, which will look granular soon after the egg is added, forms clumps and curds

Just before your pastry reaches this clumpy stage, the sound of the machine working the dough will change, so listen out

Turn the dough out onto a work surface. Very lightly and sparingly - make that very, very lightly and sparingly - knead the dough just to incorporate any dry ingredients that might have escaped mixing

Butter the tart tin and press the dough evenly along the bottom and up the sides of the tin. Don't be stingy - you want a crust with a little heft because you want to be able to both taste and feel it. Also, don't be too heavy-handed - you want to press the crust in so that the pieces cling to one another and knit together when baked, but you don't want to press so hard that the crust loses its crumbly shortbread-ish texture

Freeze the pastry for at least 30 minutes, preferably longer, before baking

Preheat the oven to 175ºC/375ºF/Gas mark 4

Butter the shiny side of a piece of aluminium foil and fit the foil tightly against the pastry

Bake the pastry for 25 minutes, then carefully remove the foil. If the pastry has puffed up, press it down gently with the back of a spoon

Bake for another 3 to 5 minutes, then transfer the pastry case to a cooling rack; keeping it in its tin

In a heavy-bottomed saucepan, slowly bring the cream and milk to a simmer

Pour the hot cream & milk mixture into the bowl, whisking continuously

Carefully strain the custard on to the cooked pastry base (don't overfill)

Slice the rhubarb into lengths and place into a pattern in the custard

Carefully put the tart tin into the oven (rearrange the rhubarb lengths if they drift in the liquid during the move!)

Bake for 40 minutes or until the top begins to brown

Remove from the oven, sprinkle a little granulated sugar over the top and allow to cool on a wire rack before slicing and serving