Ingredients :

• The apples — Choose Granny Smiths if you want a slightly tart contrast to balance the sugar. Goldens work too, but they result in something sweeter and less complex. Avoid mealy apples — they completely disappear during baking, leaving only moisture without texture.
• Brown sugar — It appears twice — in the streusel and in the batter. This is what gives the cake its slightly caramelized taste and deep color. Don’t replace it with white sugar: you’d lose half the character.
• Full-fat sour cream — The original recipe uses American sour cream. Replace it without hesitation with full-fat crème fraîche or plain Greek yogurt. Both options provide the light acidity that makes the crumb moist without weighing it down.
• Cold butter for the streusel — It really needs to come out of the fridge at the last second. If it starts softening between your fingers while you’re rubbing the dough, the streusel won’t form correctly — you’ll end up with a greasy mush instead of crunchy crumbs.