Process flour, butter and a pinch of salt in a food processor until mixture resembles breadcrumbs.
Step 2Whisk egg and 1 tbs chilled water in a bowl until combined, then with food processor motor running, add to flour mixture. Process until mixture begins to form large clumps, stopping machine before mixture forms a ball.
Step 3Turn pastry out on to a work surface and knead gently to bring together. Form into a disc for a round tart or into a log shape for a rectangular tart. Wrap in plastic wrap and refrigerate overnight or for at least 2 hours.
