Pre-heat the oven to 200°C/400°F/gas mark 6.
Roll out the pastry into a rectangle approx. 25 cm by 30 cm. Grease a deep-pan baking tray or pie dish and place the rolled out pastry into this. Put the pan into the fridge to chill while you prepare the asparagus.
Wash and trim the asparagus. If large, slice lengthways into halves.
Add the olive oil into a frying pan and gently fry the asparagus until slightly browned. When the asparagus is close to being cooked, add the chopped garlic and cook for a further 2-3 minutes. Add salt, pepper and lemon juice.
In a separate bowl, measure out the cream and add 1 teaspoon Dijon mustard and 2 teaspoons plain flour and mix well.
Take the pastry tray out of the fridge and arrange the cooked asparagus onto this in a line, leaving a small rim around the edges.
Pour the cream mixture over the asparagus and place the dish into the oven. Cook for approx. 30 minutes.