This scrumptious salad is especially delicious with garden-fresh spinach and cherry tomatoes and it makes a very satisfying summer lunch.
For the dressing:
To make the dressing, in a small bowl, whisk the mayonnaise, vinegar, and lemon juice together. Add the buttermilk and whisk again. Stir in the cheese and season to taste with salt and pepper. Taste and adjust the seasonings, if necessary. (The dressing will keep, covered, in the refrigerator for up to 1 day.)
For the salad:
To make the salad, fry the bacon in a skillet until crisp and drain on paper towels. When cool enough to handle, crumble and set aside.
Wipe out the pan with paper towels. Heat the olive oil in the pan over medium heat. Add the bread cubes and cook, stirring often, until lightly browned, 7-8 minutes. Drain on paper towels.
Combine the spinach, onion, and half of the croutons in a large shallow bowl and toss together. Pour half of the dressing over the salad and gently toss. Arrange the bacon, tomatoes, and remaining croutons over the salad and drizzle with the remaining dressing. Add a bit more pepper, if desired, and serve.