In a medium frying pan, sauté the bacon over medium heat for about 10 minutes or until it has rendered its fat and is quite crisp and a rosy brown. Drain and set aside. Using some of the bacon fat, sauté the shallots for about 1 ½ to 2 minutes over medium heat until soft and pale golden. Drain and set aside.
Bring a large saucepan of lightly salted water to a boil and blanch the Brussels sprouts for about 1 minute. They will turn a vibrant green. Pour into a colander and run under cold water until cool to stop the cooking process. Drain and pat dry with paper towels.
In a small bowl, combine the mustard, lemon juice, salt, vinegar, and olive oil. Let rest for 5 minutes before whisking in the reserved shallots.
In a serving bowl, gently mix together the Brussels sprouts and bacon. Pour in the dressing and toss. Sprinkle with poppy seeds and serve at room temperature, or slightly warmer.
Photo by Doug Bradshaw.