Preheat the oven to 375 °F / 190 °C / Gas Mark 5, no fan (if you have a convection oven, reduce the temperature by 25 degrees).
Prepare two ramekins, about 4-inch / 10 cm in diameter.
Cut the rhubarb into ½ inch / 1 cm slices (you don‘t have to peel it), mix with sugar and potato starch together.
Divide the rhubarb evenly into the 2 ramekins.
Make the crumble: Mix the sugar with flour and ground almonds together, add the softened butter, rub with your fingers, until dough is created, stir in the flaked almonds. Divide the dough with your fingers into clumps and place on top of the rhubarb.
Place the ramekins in the oven and bake for about 35 minutes, until the crumble is golden, crunchy and baked through, rhubarb filling should be bubbling.
Serve with vanilla ice cream.
Enjoy!