Pour the milk, water, eggs and salt into a blender and process on low. With the motor running, slowly add the pancake mix. Refrigerate for 1 hour, up to overnight. The mixture should have the consistency of heavy cream.
Stir together the crème fraîche, lemon juice and horseradish in a small bowl. Grate the lemon over all, stir in, cover and refrigerate.
Blanch the asparagus and set aside. To blanch asparagus, bring a pot of water to boil, then submerge the asparagus for 3-5 minutes until crisp-tender. Drain and place the asparagus in an ice-water bath.
Heat an 8-inch nonstick skillet over medium-high heat. When pan is hot, add 1/2 teaspoon oil to the pan. Lift the pan off the heat and gently swirl the oil to coat the surface. Return the pan to the heat. Pour in 2 tablespoons of the reserved batter, lift the pan and gently swirl the pan to coat the bottom with the batter. Cook until lightly browned, about 1 minute, then flip the crêpe and brown the other side. Remove the crêpe to a plate and cover with a small piece of waxed paper. Repeat, stacking the finished crêpes between waxed paper until you have used up the batter. You should have 10 to 12 crêpes.
Sautè the asparagus until hot. On each crêpe, place 3 thin asparagus spears, 1 slice of smoked salmon and roll loosely. Place 2 crêpes on each plate, drizzling the reserved lemon crème fraîche over all. Sprinkle with the chopped dill and serve.