You can’t really substitute black pudding for morcilla. The texture of black pudding is not the same, generally contains more fatty bits, and doesn’t break-up as readily as morcilla. Brindisa stocks some decent versions and the pack I brought last week from The Tapas Lunch Company (£2.15 for 200g) worked beautifully too.
Just fry the morcilla in a little olive oil and near the end of cooking add a handful of pinenuts. Top some slices of rustic bread with a little tomato sauce (mine I enhanced with a little sweet pimenton, also brought from The Tapas Lunch Company) and warm in the oven (or toast first) then top with the morcilla. My original attempt to replicate the dish included adding an egg to the morcilla before the pine nuts; not totally convinced this is what was in the original dish. To make more of a substantial meal you could serve a chorizo and tomato salad alongside.
You obviously need a wine.
The Palacio de Bornos Verdejo, 2010, Rueda, Spain from Waitrose £8.99 [Adegga / Snooth] isn’t too bad a match. Thinking maybe a bowl of freshly griddled prawns might be better… this is crisp, weighty (a touch of residual perhaps?) like a ripe, fleshier Sauvignon Blanc.
Another drinking option could be the rather excellent La Bascula Catalan Eagle 2009 an organically grown mix of Garnacha Blanca, Viognier, Roussanne, a blend which I adore. A touch too floral maybe for the morcilla but that complexity melds rather gorgeously with the spice of the chorizo in the salad.