Mix 1/4 cup each, yogurt and mustard in a small bowl. Taste and adjust mix---if no one's looking, just dip your finger in and give it a taste. You're looking for a nice balance of the tangy bite of the mustard and the creaminess of the yogurt for richness. Stir in dill and taste again. If you don't get a distinct dill flavor, add more, a little at a time. When you utter an involuntary "ummmmm," you've got it right. Set aside.
Heat a large non-stick skillet over medium high heat. Pat salmon fillets dry with paper towel and season non-skin side with salt and pepper. Add oil to pan. When it starts to shimmer, add fillets, skin side down. Cook for about 3 minutes, then turn and cook an additional 3 minutes or so, until done. Ideally, they should still be slightly pink inside.
Transfer fillets to plates. Spoon sauce over fillets and top with dill sprigs. Serve. Pass around additional sauce at the table. At our table, it kept getting passed around as we all slathered our fillets in it. Much less elegant looking than the original presentation, but oh so good.