Cube the Velveeta and place it in a large microwave-safe bowl with the Rotel and milk if using.

Microwave on high for 2 minutes, stir, then continue in 1-minute bursts, stirring each time, until smooth and fully melted, about 5 minutes. (Or combine in a saucepan and cook over low heat, stirring often, until melted, about 8 minutes.)

Stir once more and transfer to a serving bowl. Serve hot with tortilla chips.