Mashed Potatoes with Bacon and Mustard

1. In a large saucepan, cover the potatoes with water and bring to a boil. Add a generous pinch of salt and simmer over moderate heat until tender, about 20 minutes. Drain the potatoes in a colander, shaking off any excess water.

2. Meanwhile, in a large skillet, cook the bacon over moderately high heat, stirring occasionally, until crisp, about 8 minutes. Using a slotted spoon, transfer the bacon to paper towels to drain. Pour off all but 2 tablespoons of the fat from the skillet. Add the onion and cook over moderate heat, stirring, until just starting to brown, 6 to 8 minutes. Add the vinegar, mustard and celery seeds and cook, stirring, until most of the liquid has been absorbed, about 2 minutes.

3. In the large saucepan, melt the butter in the milk over moderately low heat. Remove from the heat. Press the potatoes through a ricer into the pot and mix well. Fold in the mayonnaise, bacon, onion mixture, and parsley and season with salt and white pepper. Serve right away.

Make Ahead

If you're not serving the potatoes right away, let them cool, then transfer to a bowl or large resealable plastic bag and refrigerate for up to 3 days. Rewarm the potatoes in the microwave in 2-minute intervals, stirring each time, until hot.