Slice the courgettes thinly.
Make a smooth but thick batter by adding water to the flour, while whisking. Heat the oil, in a large deep frying pan, to 'chip cooking' temperature. When ready, add half of the beer into the batter mixture and whisk firmly - the batter should foam up.
Dip the courgette slices into the foaming batter mixture (re-whisk with more beer if it sinks) and place in a large frying pan of hot olive oil (one at a time!) Cook for about 2-3 mins or until golden and crispy , turning over once during that time with a slotted spoon.. If you are unable to fit all the courgettes in the pan at the same time, then do them in batches.
Dry on kitchen paper towel and brush with garlic butter. Serve on a large plate with a generous sprinkling of grated parmesan cheese and chopped parsley