Preheat your oven to 180 °C (350 °F).
In a bowl, toss the chopped apples with lemon juice, sugar, cinnamon, and cornstarch. Divide the mixture into 4 small oven-safe ramekins.
For the crumble topping: Add flour, sugar, salt, and cinnamon to a bowl. Add the cold butter and rub everything together with your fingers until you get a crumbly texture.
Generously top the fruit with the crumble mixture.
Bake for 20–25 minutes, until golden and bubbling.
Let cool for a few minutes and serve warm – optionally with vanilla ice cream or whipped cream.