The original recipe called for white button mushrooms, but because I like crimini mushrooms more, that’s what I chose. And for the mayonnaise, I used Best Foods (also sold as Hellmann’s). Homemade would be terrific, but there’s nothing wrong with Best Foods.
Also: the flavor of this salad really deepens with time, so consider making it a day (or even two) before you want to eat it.
Heat 3 tablespoons of the oil in a 10” or 12” skillet over medium-high heat, and add the mushrooms. (If they don’t all fit in the pan at once, let the first panful wilt down a bit, and then add the rest. It’ll work out fine.) Cook, stirring often, until lighly browned, 14-16 minutes. Transfer to a large bowl, and set aside. Wipe out the skillet.
Heat the remaining oil in the skillet over medium-high heat, and add the onion. Cook, stirring often, until the onions begin to soften; then reduce the heat to low and continue to cook until lightly caramelized, 10-15 minutes. Transfer to the bowl with the mushrooms. Add the dill and eggs, and stir to mix.
In a small bowl, whisk together the mayonnaise, mustard, and lemon juice. Add a couple of spoonfuls to the mushroom mixture, and toss until evenly combined. Taste, and add more dressing as needed. (All in all, I used only about two-thirds of the dressing.) Season with salt and pepper. Depending on how deeply browned the onions are, you might also want an extra squeeze of lemon.
Pile on lightly toasted bread – preferably sourdough rye, if you’ve got some – and serve open-faced.
Yield: about 2 cups