Preheat oven to 190 degrees C. Use 2 large baking trays and grease lightly.
Place the flour in a bowl, add butter and rub in with fingertips until the mixture resembles fine breadcrumbs.
Stir in the sugar, cinnamon, diced apples and muesli. Stir in the egg and enough milk to roughly bind the mixture.
Drop 24 spoonfuls of mixture onto the baking trays, leaving space between for each to spread. Sprinkle tops with extra sugar. Bake for 15 minutes or until golden and firm to the touch.
Transfer to a wire rack to cool. Serve warm or cold. They can be kept in an airtight container for up to 2 days.