Heat oven to 200C/fan 180C/gas 6. Line a muffin tin with muffin cases. In a small bowl, use your fingertips to rub 50g of the flour together with the butter to make breadcrumbs. Stir through 1 tbsp sugar and the chopped pecans, then set aside.
In a large bowl, sift together the remaining flour, baking powder, bicarbonate of soda and a pinch of salt, then stir in the sugar and cinnamon and set aside. Coarsely grate two of the apples, then beat together with the soured cream, egg and 2 tbsp milk. Make a well in the dry ingredients and quickly fold through the wet ingredients, adding an extra tbsp milk if really dry. Don’t over-mix or your muffins will be tough. It doesn’t matter if there are lumps of flour.
Spoon the mixture into the muffin cases – they should be about two-thirds full – then sprinkle over the pecan topping. Thinly slice the final apple, then poke slices into the tops of the muffins. Bake for 20 mins or until risen, golden and a skewer inserted in the centre comes out clean.