Preheat an oven to 180°c/160°c fan (356°f/320°f).
Grease the inside of a round 10" ovenproof dish with butter then set aside.
Peel & core the apples then cut into 1-2cm pieces. As you cut the apples, place the pieces into a mixing bowl with the lemon juice, to stop them going brown.
Next, add the sugar, vanilla, cinnamon, ginger & salt to the apples & stir to coat.
Place the butter into a large saucepan then set over a medium heat & cook until browned, stirring almost constantly. This will take 2-3 minutes.
Add ⅔ of the apple pieces (& all of the liquid in the bowl) to the brown butter then cook until the apples have just started to break down. This will take around 5-10 minutes. Make sure to stir the apples regularly!
Stir in the remaining pieces of apple, cook for another 2 minutes then take the pan off the heat.Adding the remaining apples right at the end means that they will hold their shape once cooked. This gives the filling extra texture. If you're using a mix of cooking & eating apples, you'd cook the cooking apples first then add the eating apples at the end. Transfer the filling into the greased dish then sprinkle the chilled crumble topping over the top, so that the apples are completely covered.
Bake the crumble in the preheated oven for 25-30 minutes, until the topping is crisp & golden and the filling is bubbling.I'd recommend cooking the crumble on a baking tray, just in case any juices bubble over! Once baked, spoon the crumble into bowls then serve with scoops of vanilla ice cream or a generous amount of hot vanilla custard.