Preheat oven to 425ºF (220ºC). Place rack in the centre of the oven. Generously butter the bottom and sides of four medium-sized ramekins (or one large soufflé pan) with 1 ½ Tbsp (20-25 mL) of butter. Sprinkle with bread crumbs, swirling to generously coat the bottom and sides of the ramekins. This coating will allow the soufflés to rise without sticking to the sides of the dishes.
Melt the remaining 1 ½ Tbsp (20-25 mL) of butter in a large saucepan over low heat. Whisk in flour and mustard and cook, whisking constantly for 3-5 minutes. Slowly whisk in milk and cook until thick and smooth, an additional 3-4 minutes. Remove from heat and season with salt, pepper and nutmeg. Add sliced asparagus and chopped turkey meat. Pour soufflé base into a large bowl. Whisk in egg yolks a few at a time until smooth. Stir in grated Asiago and chives until well incorporated. Using a hand mixer (or stand mixer), whip 12 egg whites in a separate bowl until stiff peaks form. Quickly mix about one-quarter of the egg whites into the soufflé base. Then gently fold in the rest into the soufflé base just until incorporated. Pour into ramekins and bake for 17 minutes and serve before they start to fall.