Ingredients :

• The apples — Go for Golden Delicious or Reine des Reinettes — they hold up well during cooking and won’t turn into a shapeless mush. Granny Smiths also work if you want more acidity. Avoid Fuji, which are too sweet and too firm.
• The red berries — Frozen is perfectly fine — no need to thaw, they will release their juices during baking anyway. A mix of raspberries, blackcurrants, and redcurrants gives a more complex result than strawberries alone.
• The butter — It must be cold, taken out of the fridge at the last moment. If you use it softened or melted, you’ll get a compact paste instead of crumbs — and that’s a fail.
• Brown sugar — Prefer it over white sugar. It brings a slight licorice taste and a deeper amber color. The topping will also be slightly crunchier.