To make the muffins, whisk together the plain flour, warm milk, warm water, melted butter, salt and dried yeast. Cover and leave in a warm place for 1 hour.
Grease 8cm rings with butter, place into a frying pan and spoon in the muffin mix, cooking gently on both sides for 3-4 minutes.
To make the hollandaise, whisk the egg yolks in a large bowl over a pan of simmering water, with the vinegar. Slowly add the butter whisking continuously and then add the lemon and keep warm.
Split and toast the muffins, top with brown crab (mixed with crème fraiche and lemon) then add the baby spinach, followed by the white crab meat. Spoon over the hollandaise, then sprinkle over the chives and serve.