Heat oven to 180C/160C fan/gas 4 and line a muffin tin with nine cases (alternatively, use squares of baking parchment). Mix the oil, yogurt, honey, eggs and vanilla in a jug. In a bowl, combine the flour, bicarb, mixed spice and ¼ tsp salt. Pour the yogurt mixture into the flour mixture and add the apple and carrot, as well as any extra ingredients you’re using. Mix with a spatula until well combined, then spoon the mixture into the muffin cases.