Peel the cherries and crush them with a fork, there may still be some chunks inside. Place the cherries, jam and cornstarch in a saucepan and bring to the boil. Stir well. Leave to cool in the fridge.
Mix the butter with the oats, almond flour, flour, baking powder and salt until you have a crumbly mixture. Divide the dough in two. Whisk the egg into one of the doughs until you have a nice smooth dough, this will be the base of the cake. Grease a 20 x 30cm rectangular baking tin and line with baking paper.
Press the first half of the pastry into the tin until the base is completely covered, then spread the cherry layer on top and finally the crumble topping. You may need to crumble the cake a little with your hands to get the right crumbly texture. Sprinkle with almonds and bake in a preheated oven for 30 to 35 minutes until golden brown.
Serve with a little icing sugar and a scoop of vanilla ice cream.