Grease a medium ovenproof dish.
Cut the croissants in half - if they are not stale, lightly toast them. Spread some soft butter on all pieces, then arrange them in the dish.
Make the cherry spread. Put the ingredients in a pan. Add some cherry juice or the jus of the defrosted cherries. Bring to the boil and cook until you get a jam-like mixture. Let it cool.
Make the custard. Beat the eggs and egg yolk in a bowl with the sugar. Put the milk and cream into a saucepan and heat it just to the boil, then take it off the heat. Gradually pour it over the egg, while whisking.
Spread the jam-like mixture over the croissants, then scatter the fresh sour cherries on top.
Pour over the custard and rest for about 20 minutes to allow the custard to soak into the croissants.
Preheat the oven to 170°C.
When hot, cover the dish with foil and put it in the oven for 20-25 minutes. When the custard has set, remove the foil.
Scatter the sugar on top and bake for another 5-8 minutes or so, until the top caramelises.
Turn off the oven. Scatter the almond flakes on top and put the dish back in the oven for a minute or so for the almonds to brown a bit.