Bring the broth to a simmer. Melt 1 tablespoon butter and the olive oil together in a large pot. Add the shallot and cook until it is clear. Add the arborio rice and stir to coat, cooking for a minute or two until it turns opaque. Add a cup of broth and cook, stirring, until almost evaporated. Continue with a ladleful of broth (1/2 cup) at a time, stirring all the while. When you are down to a couple of ladlefuls of the broth left to add, add the asparagus slices. Continue adding broth until it is used up. When the last ladleful of broth has been absorbed, stir in the final 2 tablespoons butter, and set risotto aside, covered, while you grill the fish.