Rub the butter into the flour until the mixture resembles fine breadcrumbs. Add just enough cold water to bring the pastry together into a pliable dough, being careful not to over-knead it.
Wrap in clingfilm and chill in the fridge for 30 minutes.
Meanwhile, cook the broccoli in boiling salted water for 3 minutes, then plunge into cold water and drain well. Leave to dry on kitchen paper.
Preheat the oven to 200°C (180° fan) | 400F | gas 6.
Roll out the pastry and use it to line a 23 cm | 9-inch round tart case. Prick the pastry all over, line with greaseproof paper and fill with baking beans or rice.
Bake the pastry for 10 minutes then remove the paper and baking beans. Brush the inside with a little of the beaten egg, then return to the oven for 8 minutes or until crisp.
While the pastry is baking, whisk the rest of the egg in a large jug with a pinch of salt and pepper, the double cream, lemon zest and dill.
Arrange the salmon and broccoli in the pastry case, then pour in the egg mixture.
Reduce the oven temperature to 170°C (150° fan) | 325F | gas 3. Bake the quiche for 30 - 40 minutes or until the filling has set with just a slight wobble in the centre. Serve warm or at room temperature.