Cut cheese into 6 wedges. Carefully remove rind from cheese; discard rind. Chop cheese; let stand at room temperature while potato cooks.
Place potato in a large Dutch oven; cover with water. Bring to a boil. Reduce heat; simmer 12 minutes or until tender. Drain in a colander; return potato to pan. Add cheese, milk, salt, and 3/4 teaspoon pepper; mash with a potato masher until smooth. Garnish with chives and additional pepper, if desired.