How to Make It
Melt butter in a 2- to 3-quart pan over medium heat; add shallots and stir just until limp, about 2 minutes. Add flour and stir until pale gold, 2 to 3 minutes. Remove pan from heat and whisk in broth, evaporated milk, and basil. Whisk or stir mixture over high heat until boiling and thickened, then reduce heat to medium-low and whisk in tomato paste and salt to taste.