Line a large mixing bowl with a clean tea towel or muslin cloth. Grate potatoes and courgettes coarsely directly into the prepared mixing bowl. Add the chopped onions.
Lift the tea towel with your vegetables out of the bowl and, holding it over the sink, squeeze out the moisture by twisting the tea towel. The more you squeeze out, the crispier your fritters will be.
Tip the vegetables into a large bowl, crack an egg in, add the flour, garlic powder and some salt and pepper. Mix well.
Heat a generous glug of oil into a large frying pan (or use more than one at the same time to speed up the process).
Drop large tablespoons of the mixture into the pan and spread each out into a thinner layer. Fry for about 4 minutes on each side on medium heat until golden brown and crispy.
Remove the fritters from the pan and place on a wire rack or a kitchen towel to get rid of access oil (but only for a minute, or they'll get soggy if kept on a kitchen towel for too long). Do not stack the fritters.
Fry the next batch until you have no mixture left.
Serve fritters with a dollop of sour cream and a side of green salad for a light lunch. Alternatively, arrange on the board with various dips (suggestions in the text above) and salsas for a great party platter!