Preheat oven at 190°C/370°F. Grease a baking dish.
Cut up the apples in thin slices and place them in a bowl. Add the sugar, cornstarch, lemon juice and cinnamon. Toss to combine and spread the mixture evenly in the prepared baking dish.
In another bowl mix the flour, baking powder, sugar, salt and almonds (optional). Rub in the butter until the mixture is crumbly and spread it over the apples. Bake for 30-35 minutes or until golden brown.