Slice the black pudding, roughly 3mm thick, then thinly slice the apple (core and all), discarding the seeds. Halve the lemon.
Heat a little oil in a pan on a medium-high heat. Fry the black pudding for 2 to 3 minutes each side, or until the surface is browned. Break up a few slices, let them crisp up, then move to kitchen paper on a plate, to drain.
Add the apple and half the lemon juice to the pan. Cook for 1 minute or so on each side, or until starting to caramelise.
Add the maple syrup and toss to coat the apple. Cook for 1 minute more, or until thick and glossy. Return the black pudding to the pan to warm.
Toast your crumpets.
In a jar, shake the rest of the lemon juice with twice as much extra virgin olive oil and a little sea salt and black pepper, then dress the watercress.
Top the crumpets with black pudding and apple and serve with the cress.