Simmer potatoes with bay leaves in a large pot of salted water until falling apart when poked, 20 to 25 minutes. Meanwhile, in a medium pot, whisk milk and mascarpone. Heat over low heat until simmering. Stir in pepper; keep warm.
Drain potatoes, discarding bay leaves. Return to pot over very low heat and cook, stirring, until dried and crumbling. Remove from heat. Beat with a mixer until smooth. Beat in mascarpone milk, a third at a time. Stir in chives and season with salt.
Note: Nutritional analysis is per serving.