Microwave milk in a 1-quart Pyrex measuring cup until steamy. Meanwhile, melt butter in a large saucepan over medium heat.
Whisk in flour and turmeric until smooth, then whisk in milk until creamy and thick.
Whisk in cheese. (Dip can be refrigerated in an airtight container up to 3 days.) When ready to serve, return cheese sauce to saucepan; stir in salsa and lemon juice, and slowly rewarm. Adjust seasonings, including salt and pepper to taste, and serve.
