1Fill stockpot or large Dutch oven half full of water; add table salt until water is almost salty to the taste. Heat water to boiling over medium heat. When water is boiling, add pasta; cook as directed on package until al dente. Remove from heat; drain.
2Meanwhile, in 3-quart saucepan, melt butter over medium heat. Add flour; beat with whisk until flour begins to cook and smells slightly nutty, 30 to 50 seconds. Quickly add half-and-half; beat with whisk to combine. Heat to boiling. Reduce heat to low; simmer 5 to 8 minutes or until thickened. Remove from heat; let stand 1 minute.
3Pour white sauce into blender. Add basil leaves; cover and blend until basil is in tiny pieces. Pour back into saucepan. Heat over low heat until mixture simmers. Stir in lemon peel, lemon juice, garlic salt, and the salt and pepper to taste. Remove from heat. Add pasta, tomatoes and cheese; toss.