Whisk the margarine, milk, egg and vanilla together with a fork, then add to the flour mixture.
Stir gently until the mixture is just combined; don't over beat or the muffins will be tough.
Spoon mixture into the prepared pan.
Bake for 20 minutes or until muffins are well risen and spring back to the touch.
Leave in the pan for a few minutes then lift out onto a wire rack to cool, or eat while still warm.
HINT: Don't leave the muffins in the tins too long after baking - they need a few minutes to firm up, but leaving them to sit for too long will cause them to stick. To remove, run a knife around each muffin then gently prise from the tin