Freeze baking tray. Grease and line the rimmed baking tray with parchment. Flour work surface and work out chilled pastry to soften in oder to become pliable. Roll it out into a large 18X16-inch/45X35cm sheet (dust flour as often as necessary). Use the frozen baking tray to cool off pastry if needed.
Prick pastry sheet well and all over.
Drape the prepared rimmed tray and gently press around the edges. Freeze for 10 minutes and trim off excess dough. Freeze.
Spread almond cream evenly.
Cover the almond cream with thin slices of stall brioche, panettone or sponge. It acts like a sponge soaking up the excess juices released by the fruit during baking.
Plum Slab Montage
Wash plums. Cut in half, remove the pit and quarter.
Arrange fruits next to each other.
Sprinkle raw sugar.
Baking
Preheat fan oven to 300ºF/150ºC. Bake pie for 75 minutes. Let cool for 4 hours before eating.
How To Unmold Slab Pie Safely
This is my never-fail technique. It works for all pies. First, and when the pie is at room temperature, freeze it for 3-4 hours. Then run a small offset spatula around the edges.
Cover pie with parchment and a baking tray, and reverse.
Gently tap and remove the sheet pan.
Top with a cooling rack and flip again.
Cut into 25X100g, or 50X50g portions.
Enjoy!
Storage
Once baked and portioned, plum pies can be kept frozen for up to 2 months. 2 hours before serving: throw frozen pies in your preheated oven (400ºF/200ºC) for 2 minutes. Turn oven off, and leave them in for 10 minutes more. Remove pies from the oven, and leave them at room temperature for an hour before serving.