To make the pastry, sift the flour in a large mixing bowl, add the butter and lard cut into cubes, and use your fingertips to rub everything together until you get a mixture that resembles breadcrumbs.
Add the milk, and knead it into a dough that does not stick to the hands.
Cover the dough in clingfilm, and refrigerate for 30 minutes.
Transfer the dough to the work surface, and use a rolling pin to roll it into a large enough circle that can cover a flan or quiche tin.
Lift the pastry onto the tin, and press down gently into the corners.
Cover the pastry with clingfilm again, and leave it to rest in the fridge for a further 20-30 minutes.
Line the pastry with non-stick baking paper, and fill it with baking beans or dry pulses.
Bake in the preheated oven at 190 degrees Celsius (375 Fahrenheit) for 25 minutes, remove the paper and beans, and leave it to bake for a further 5 minutes uncovered until lightly golden.
To make the filling, crack the eggs into a jug, and use a fork to beat them well.
Pour in the milk and cream, add the salt, pepper and tarragon, and give it a good stir.
Scatter half of the cheese over the bottom of the pastry, followed by the spinach and broad breans.
Pour over the egg mixture, making sure it's evenly dispersed, top with the remaining cheese and bake at 160 degrees Celsius (320 Fahrenheit) for 25 minutes or until the filling is set and lightly golden.
Leave it to cool before slicing.