Chop the rhubarb into 3cm chunks and place in a 30cm x 35cm roasting tray.
Use a speed peeler to zest the orange into the tray and squeeze over the juice. Split the vanilla pod and scrape in the seeds, scatter over the sugar, and scrunch everything together.
Bake for 20 to 25 minutes, or until just starting to soften, then remove the tray from the oven and leave to cool.
Once cool, tip the rhubarb into a sterilised 1 litre jar (see tip below)
Pour in the gin (don’t forget to save the empty gin bottle as you’ll need this later) and seal the jar tightly. Tip upside down to ensure everything is gently mixed.
Store in a cool, dark place for 3 to 4 days, for the flavours to get to know each other. When it’s ready, strain the mixture back into the empty gin bottle. It will keep in a cool, dark place for 1 month.
Serve the gin over ice with tonic water and a slice of orange or lemon, or shake up into one of your favourite cocktails.