In a stand mixer, use a paddle attachment at medium speed to cream the softened butter and icing sugar. Mix until smooth and creamy – this should take about 2 minutes.
Add egg and half of the flour. Mix on a slow speed until the flour is incorporated.
Remove the bowl from the machine before adding the ground almonds and the remainder of the flour.
Bring the pastry together and mix by hand but avoid overworking it.
Wrap your pastry with cling film / plastic wrap before refrigerating it for between 30 minutes and a couple of hours.
Grease 1 x 25cm (10 inch) loose bottomed flan tin or 8 x 9cm (3 ½ inch) individual tart tins.
Roll out your pastry between two sheets of baking parchment to prevent it from sticking to everything.
Make sure the pastry circle is appropriately sized for your flan tin. The circle needs to be a touch larger than the diameter of your flan tin plus twice the tin depth. Ideally, the pastry thickness should be about that of a £1 coin (3 mm / ⅛ inch.)
Carefully line your flan tin with pastry, gently pressing the pastry into the corners, sides and edges. Try not to stretch the pastry, patching any cracks that might appear.
Trim off excess pastry but leave the sides slightly higher than the flan tin in case of shrinkage.
Prick the bottom of the pastry case with a fork before popping in the fridge for at least 15 minutes.
Line your pastry case (or cases) with baking parchment and fill with ceramic beans, rice or dried beans.