Put a cast iron fry pan or heavy non-stick pan over a high heat and allow it to get hot.

Cut the lemon into quarters and place them cut side down in the hot pan. Once the lemon is charred turn to char the other cut edge.

Remove from the pan and set aside to cool.

put the rosemary, coriander seeds and gin into a cocktail shaker or measuring jug.

Use a wooden spoon to lightly bash the aromatics.

Divide the ice between two large round bottomed glasses.

Strain the gin into your glasses.

Top up with tonic water, stir briefly and add in your charred lemon quarters.

Serve  immediately with a small pinch of whole peppercorns.