Preheat oven to 180 degrees Celsius and line a baking tray with baking paper. Sprinkle 1 tablespoon of flour of the baking paper.
Place puff pastry onto the kitchen table to thaw. While that is happening, wash and dry apples and then cut into quarters. Core apples and then slice each quarter into 5 thin slices.
Put apples in a bowl as you cut them, sprinkling them with the juice of half a lemon as you go to help keep them browning.
Once the pastry has thawed, sprinkle it with 2 tablespoons of flour and 2 teaspoons of sugar. (The flour will help absorb the juices from the fruit.)
Arrange the apples over the top of the pastry in any pattern that you like, leaving an inch border around the edges. You can start from the centre and work outwards or place slices in a pretty but random pattern as I have.
Fold the pastry in from the sides, creasing it where necessary and tucking in the corners.
Sprinkle over the almonds and then the juice of the second half the lemon and the remaining teaspoon of sugar.
Use a pastry brush to paint the exposed pastry with the egg or milk wash and then bake the galette in an oven for 35-40 minutes.
Leave to cool slightly in an open oven and then serve with ice cream or cream.