Heat oven to 120C/100C fan/gas 1/2. Mix the flours, bicarbonate of soda and 1/2 tsp salt together in a bowl. Whisk the buttermilk, egg and 3 tbsp melted butter together in another bowl, then gradually whisk into the dry ingredients to make a smooth batter.
Heat a non-stick frying pan over a medium heat. Add the remaining butter and the oil, plus the asparagus, and fry, turning, for 3-4 mins until almost tender.
Turn the heat down and scoop out all but 6 of the asparagus spears. Arrange the 6 left in the pan into 2 groups of 3. Use a ladle to spoon a little batter over each group of asparagus, to make 2 round pancakes, with the asparagus hidden underneath. Cook the pancakes until bubbles appear on the surface – about 2-3 mins. Flip over and cook for 1-2 mins more until golden and set. Remove and keep warm in the oven while you use the remaining asparagus and batter to make another 10 pancakes.
Pile 3 pancakes on each plate and add a pile of smoked salmon. Serve with some soured cream, a good grinding of black pepper, and lemon wedges for squeezing over.