To make ricotta: Combine milk, buttermilk, and salt in a large, nonreactive pot and bring to a gentle simmer. Cook, without boiling, for 5–8 minutes. Meanwhile, line a strainer with a double thickness of cheesecloth. Pour curds (solids) and whey (liquids) through strainer. Let mixture drain for 1 hour. Transfer mixture to a bowl and fold in lemon zest, garlic, pepper, and herbs. Keep ricotta for up to 5 days in the fridge, in a covered container. (Makes about 2 1/4 cups.)