Gently heat the milk and oil in a small pan. Whisk with a fork to combine.
Place the flour, salt and baking powder in a mixing bowl. Pour in the warm liquid and stir with a spoon until it starts to come together. Continue to bring the dough together with your hands. You want the dough to be soft and slightly sticky. The consistency will vary depending on the type of flour and liquid you have used. If it’s too sticky, add a touch more flour. If it’s too dry, add a touch more liquid.
Turn out the dough onto a lightly floured surface and knead for 1-2 minutes, until smooth.
Divide into 6 equal pieces (I weigh mine to divide it equally). Use your hands to roll them into balls and place on a chopping board. Cover with a clean tea towel and leave to rest for 15 minutes.
Pre-heat a dry frying pan (skillet) on medium-high heat.
Take one dough ball and coat in flour. Place on a lightly floured surface and using your fingers, press it into a thin disk. Use a rolling pin to roll it into a circle with a 23cm / 9” diameter. (To achieve a circular shape, I roll from the centre of the circle to the outer edge, in an anti-clockwise motion).
Lay the rolled dough over the rolling pin and transfer to the hot pan. After a short while, the dough should start to bubble a little. When this happens, flip the tortilla over and continue cooking until brown spots appear on the underside. If the tortilla is browning too quickly, turn down the heat a touch. (I have an electric hob and I cook mine for 40 seconds on the first side, and 20 seconds on the second).
Transfer the cooked tortilla to a plate lined with a piece of kitchen paper or a clean tea cloth. Cover with a lid slightly larger than the plate (I don’t have a lid large enough so I use an upturned frying pan!) This will help to keep the steam in and prevent the tortillas from drying out.
Repeat the process with the remaining dough balls, adding them to the plate once cooked and covering with the lid.
If not using immediately, allow the tortillas to cool completely then store flat in an airtight container in the fridge, where they will keep for up to a week. They will stiffen up over time but heating them through will return them to their pliable state.