Gently beat the eggs in a mixing bowl and season to taste with salt and pepper. Add the grated parmesan, cream, chives and seasoning, whisk till creamy then lightly swirl in the harissa paste, set aside.
Melt the butter in a small frying pan. Pour in the egg mixture and swirl pan in circular motions so egg mixture evenly coats pan, then add crumbled feta, olives, basil leaves and chives, cook for a few minutes until the omelette is lightly set. Tilt the pan to spread any uncooked egg around. Repeat the process until eggs are just set but the omelette is still soft in the centre (to quicken up process cover with a lid).
Fold the omelette in half, then remove pan from heat and tilt it slightly to move the omelette to the edge. Slide the omelette onto a serving plate. Sprinkle over basil leaves and a shaving of parmesan.