1. Preheat the oven to 180°C (160°C fan) / 350°F / Gas 4. Line a muffin tin with paper cases (this makes about 12 standard muffins, or ~24 mini muffins).
2. In a bowl, mix flour, sugar, and ground cinnamon. Rub in the butter with your fingertips until the mixture resembles coarse breadcrumbs. Set aside in the fridge while you prepare the batter.
3. Peel, core, and finely dice 1–2 apples (about 1.5 medium apples). Toss lightly in a little flour to stop them sinking in the batter.
4. In a large bowl, whisk together flour, nutmeg, ground cinnamon, salt, and baking powder.
5. In another bowl, whisk together maple syrup, melted butter (cooled slightly) Greek yogurt, 2 eggs, vanilla extract, and milk until smooth.
6. Pour the wet mixture into the dry ingredients. Gently fold until just combined (don’t overmix — a few lumps are fine). Fold in the diced apples.
7. Divide the batter evenly between muffin cases. Sprinkle a generous spoonful of crumble topping over each muffin.
8. Bake for 18–22 minutes (mini muffins: ~12–15 minutes), or until golden on top and a skewer inserted in the center comes out clean.
9. Let muffins cool in the tin for 5 minutes, then transfer to a wire rack. Delicious warm, but they also keep well in an airtight container for 2–3 days.
