1. Cover potatoes and garlic with 2 inches water in a large pot. Bring to a boil; season with salt. Reduce heat to medium and simmer 5 minutes. Add pumpkin and simmer until just tender, about 15 minutes. Remove garlic; drain.

2. Add butter and oil to pot and heat until butter melts. Add onion and chard stems; cook, stirring occasionally, until onion is translucent, about 8 minutes. Add chard leaves, milk, and nutmeg; season with salt and pepper. Simmer, partly covered, just until chard is tender, about 3 minutes.

3. Remove from heat and stir in potatoes and pumpkin, smashing lightly with the back of a spoon but leaving some larger pieces. Season with salt and pepper; serve.