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

Peel the pears, leaving them whole

Bring water, sugar and the juice of the lemon to a boil in a saucepan just large enough to hold the pears

Add the pears to the boiling syrup, lower the heat so the syrup simmers and gently poach the pears until they are tender when pierced with a knife - about 15 minutes

Cool the pears to room temperature in the syrup

Put the butter and sugar in the bowl of a food processor and process until the mixture is smooth and satiny

Add the ground almonds and continue to process until well blended

Add the flour, cornflour and egg. Process until the almond cream is homogeneous

Add the rum or vanilla and process just enough to blend

Fill the baked pastry case with the almond cream, spreading it even with an offset metal icing spatula

Thinly slice each pear half crosswise, lift each half on a spatula and place carefully on to the almond cream to form an attractive pattern

Bake the tart for 50 to 60 minutes, or until the almond cream puffs up around the pears and browns

Transfer the tart to a wire rack to cool to just warm or to room temperature before removing it from its tin

Allow to cool completely before serving