Add milk, vanilla extract and vinegar (or lemon juice) to a jug, stir and set aside.
In a large mixing bowl, add the flour, sugar, baking powder and salt, then mix well.
Add the raspberries and mix well.
Preheat the air fryer to 180 or 350f (see notes for oven baking tips) for 5 minutes.
Add the oil to the jug of milk and stir, then pour into the dry ingredients until just combined (do not beat or overmix, just gently use a folding over motion).
Spoon the muffins into silicone muffin cases or a lined muffin tin, if you have one that fits your air fryer and bake in the middle shelf of your air fryer or in your basket for 20 minutes. Some make take a little less time or a little longer.
Test a muffin with a toothpick or skewer, inserted into the middle of the muffin to see if it is ready. There may be raspberry clinging to it but there shouldn't be batter. If there is batter pop them in longer.
Once baked, remove from the air fryer and cool on a baking rack in their cases.
While they are cooling, make your icing, if you are adding a drizzle. Add icing a couple of spoonfuls of icing sugar to a small bowl and add just a little water, less than you think you need (keep stirring), you want it to be thick and white. Add just a drop or two extra at a time. If you add too much just add some more icing sugar.
When the raspberry muffins are cool, carefully remove from the cases and drizzle with the icing.
Enjoy!
Notes
If baking in the oven
Preheat to 180c/160c fan/350f/gas mark 4.
Line a 12-hole muffin tray with muffin or cupcake cases.
Bake for about 25 minutes, check them after 20 minutes.
Frozen Raspberries
You can add frozen raspberries straight in, but as these are moist muffins, it's best to defrost and pat with kitchen paper to remove any excess moisture.
Storing muffins
These muffins can be stored in an airtight container on the countertop for a couple of days or in the same container in the fridge for 4-5 days.
Freezing Muffins
Flash freeze them on a tray, then pop them in a freezer bag or tub for up to 2 months.
Take them out the night before you want one for breakfast or to add to lunch boxes and leave in the fridge overnight to defrost.