Put the milk and lemon juice in the bowl, whisk together and let sit for 5 minutes.
Add the olive oil and eggs and whisk together.
Sift the plain flour, wholemeal plain flour, baking powder and a pinch of salt and pepper into the bowl and mix together. If there's any bran left in the sieve, tip that in too.
Add the grated cheese, tomatoes, bacon and red onion. Stir together.
Divide the batter between two 4-hole muffin trays. You can fill the holes generously as these muffins rise up without spreading.
Preheat your air fryer according to the manufacturer's instructions (mine defaults to 4 minutes at 205C).
Put the first muffin tray in the air fryer basket. Set the air fryer to 170C and cook for 20 minutes until risen and golden.
Cool the muffins in their tray on a wire rack for a few minutes, then gently remove them from the tray and stand direct on the rack to continue cooling. These muffins are delicious warm or cold.