Flaked hot-smoked salmon stands in for bacon in this twist on an always-popular dish. Originally developed as a side, this has become a favorite breakfast in our test kitchen.
Prepare an ice-water bath. Bring potatoes to a boil in a large pot of water; season generously with salt. Slowly add eggs to water. Cook eggs 7 minutes, then remove with a slotted spoon and transfer to ice-water bath. Continue to cook potatoes until easily pierced with the tip of a knife, about 3 minutes more. Drain and let cool slightly.
Meanwhile, in a large bowl, whisk together mustard, lemon juice, and onion. Gradually whisk in oil. Fold in potatoes and salmon; transfer to a platter. Peel eggs; halve crosswise. Arrange on top of salad. Season eggs with salt and pepper; sprinkle with tarragon and serve.