1. Crack the eggs into a bowl and whisk them lightly with a fork. Season with a pinch of salt and pepper according to your taste.

2. On the medium heat frying pan, cook sliced onion until soft and brown and add a pinch of sugar to caramelize it. 

3. Heat a non-stick frying pan over medium-high heat. Add the butter and allow it to melt, ensuring it coats the bottom of the pan evenly.

4. Once the butter starts to sizzle, pour in the beaten eggs. Allow them to set for a moment until the edges begin to cook.

5. Using a rubber spatula, gently push the cooked edges towards the center while tilting the pan to let the uncooked eggs flow to the edges. Continue doing this until there’s very little uncooked egg left on the surface.

6. Add the Boursin cheese and caramelized onion to one half of the omelette.

7. Carefully fold the other half of the omelette over the fillings, creating a half-moon shape. Gently press down with the spatula to seal the omelette.

8. Cook for another 30 seconds to 1 minute to ensure the fillings are warmed through and the omelette is cooked to your desired level of doneness. If you prefer a runny center, cook it for less time; for a fully cooked omelette, cook it a bit longer.

9. Slide the omelette onto a plate and serve immediately. You can garnish it with chives and crushed salty chips.