Step 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.

Step 2

In the same saucepan, melt the butter in the milk over moderately low heat. Remove from the heat and stir in the cheese. Press the potatoes through a ricer into the pot and mix well. Fold in the mayonnaise and jalapeño and season with salt and white pepper. Serve right away.