Method
Heat the oven to 170°C/150°C fan.
Place all the ingredients for the patties in a large mixing bowl and work them together with your hands for a minute or two. This will help the mixture bind and give the burgers a good texture. Shape the mixture into 8 patties, no more than 2cm thick, then cover and chill until ready to cook.
Meanwhile, halve the tomatoes and place them cut-side up on a baking sheet. Season with salt and pepper and drizzle over the olive oil.
Place the tomatoes in the oven for about 1 hour, or slightly longer if you like them really intense.
Take half the watercress and, discarding any really coarse stalks, chop it finely with a knife. Stir the chopped watercress through the mayonnaise.
Cook the burgers on a barbecue or in a large, lightly oiled heavy frying pan for 4–5 minutes on each side, or until cooked through. When they are almost ready, crumble the blue cheese over the burgers and allow it to melt for a minute or so.
To serve, place a rabbit burger in each bun, top with a spoonful of watercress mayonnaise and a couple of slow-roast tomato halves, then finish with the remaining watercress.