Melt about 1 teaspoon butter in a small sauté pan over medium heat. Add onions and sauté onions until limp and just slightly brown at the edges. Set aside to cool.
Combine softened cream cheese, lemon juice, water, sugar and salt in blender or food processor. Process until smooth and creamy. Blend in onion. Add chopped fresh basil and pulse until pieces are evenly distributed. (Add an extra tablespoon of water if mixture seems too thick to blend.) Set completed dressing aside. (about 1 ¾ cups dressing), Preheat oven to 350˚F. Spread butter lightly (½ to ¾ teaspoon per side) on both sides of the bread slices. Cut into ½ inch cubes and place in a single layer on a baking sheet. Bake about 15 minutes, stirring occasionally, until cubes are golden brown. Remove from oven and set aside.
Sauté bacon in a large skillet until crisp. Transfer to a paper-towel lined plate. Set aside to cool.
In a large bowl combine lettuce thoroughly with about 1 cup of the basil dressing. Gently stir in, tomatoes, bacon and croutons. Add more dressing per taste. Serve immediately.