Preheat the oven to 180C/350F. Line a muffin tin with 10 deep paper cases. Sift the flour into a large bowl with the baking powder and salt, then stir in the oats.
Cream together the butter and sugar in a separate bowl until light and fluffy, then beat in the egg and lime rind.
Make a well in the centre of the dry ingredients and pour in the buttermilk. Add the butter mixture, blueberries and carrots and quickly mix everything together with your hands until just combined. Don’t overwork the batter.
Heap the mixture into the paper cases filling them about two-thirds full. Bake for 20 minutes until well risen and golden brown. Leave to cool for 5 minutes, then serve warm or transfer to a wire rack and leave to cool to use later in the day.