Take 1 sheet of filo and brush with a little melted butter. Sprinkle over half the pistachios to form a square measuring about 12 x 12cm in the centre of the sheet. Sprinkle over half the sugar and dot half the clotted cream on top of the pistachios. Starting at the top left corner, fold the corner into the centre, then fold the bottom right corner into the centre. Fold the two remaining corners into the centre, overlapping them slightly to end up with a square.
Put a large frying pan on a medium-high heat and brush with half the remaining melted butter, then lay the katmer in the pan seam-side down. Cook on either side for 1-2 mins or until golden and crisp. Repeat the process for the other katmer.
Cut the crisped katmer in half, so you have four pieces. Divide the ice cream between two of them, lightly pressing it down, then top with the remaining pieces of pastry to make two sandwiches. Halve them again to make four pieces. Serve straightaway, sprinkled with more pistachios, grapefruit segments or other seasonal fruit.