Preheat the oven to 230°C/fan 210°C/gas mark 8. Pour the oil in each hole of the muffin tin. Place in the oven until the oil is very hot.
Mix the plain and gram flour together. Gradually pour in the milk, whisking as you go, until the mixture is frothy.
Remove the tin from the oven and pour in the mixture so that each hole is filled halfway up. Return to the oven and bake for 20 minutes until well risen and golden. Make sure you don’t open the oven door until they're ready, or they're likely to sink.