Preheat the oven to 180°C/160°C fan/350°F.
In a saucepan over medium heat, combine 150g of the cherries with the sugar and cook for around 2 minutes to release their water, stirring regularly until the cherries defrost. Once the cherries start to break down, lower the heat and cook until the mixture is thick and jammy, around 5-10 minutes.
Add the remaining 100g cherries to the jammy compote and stir to combine. Cook for another 2 minutes to defrost, then remove from the heat so they keep their shape. Leave to cool as you roll out the pastry.
On a floured work surface, roll out the puff pastry into a rough circle. Line a baking tray with baking paper and gently lift the pastry onto it. It doesn't matter if the edges are hanging off.
Pile the cherry compote into the centre of the pastry circle, spreading it out so it's a flat layer of cherries. Make sure you leave a 5cm border around the fruit.
Fold the edge of the pastry over the cherries in segments. It will look messy but that's good, it's a messy looking tart. Go around the tart folding over the segments of pastry so they are overlapping covering the edges of the fruit.
Brush the pastry all over with egg wash then sprinkle with the flaked almonds. Slide the tray into the oven and bake for 20-25 mins until the tart is crisp and golden, and the cherries are leaking some juice.
Sprinkle with icing sugar before serving. Eat with crème fraiche flavoured with a tiny drop of almond extract if you wish.