You can definitely make the components of this dessert separately, in advance. But once assembled, it should be served within a day. Choux pastry dough - Can be made 1 day in advance and stored in the fridge, ideally in a sealed pastry bag. Allow it to come to room temperature before you pipe it to make Paris Brest pastries. Baked, unfilled choux pastry rings - Baked and unfilled pastry cases can be stored for 1 - 2 days in the fridge. But up to 1 month in the freezer. Place the thawed pastry cases on a baking tray and bake at 300 F for a few minutes to "re-crisp" the shells. This will make them taste a little better, as choux pastry does become stale quickly. Praline paste - Praline paste will last in the fridge for a few months. So you can make this in advance. It'll last for at least 1 year in the freezer as well. Pastry cream - Pastry cream will only last 3 - 4 days in the fridge. I do not recommend freezing pastry cream. Praline mousseline cream - Mousseline cream prepared with freshly made pastry cream will also only last 3 - 4 days in the fridge. If the pastry cream was made a couple days before, this will also shorten the lifespan of the mousseline cream. Allow the mousseline cream to soften to room temperature and re-whip for a few minutes to make sure it's creamy before you use it.