- COOK THE PASTA AND ASPARAGUS: Bring a large pot of water to a boil over high heat. Add the 2 tablespoons salt and the pasta. Cook, stirring occasionally to prevent sticking, until the pasta is al dente (tender but firm to the bite), according to the package instructions.
- About 4 minutes before the pasta is done, add the asparagus to the boiling water and cook until crisp-tender. Drain the pasta and asparagus, rinse under cold running water and drain again.
- MAKE THE DRESSING: Meanwhile, in a large bowl, whisk together the garlic, vinegar, mustard, mayonnaise, the 1/2 teaspoon salt and the pepper. Gradually whisk in the olive oil until smooth. Add the pasta and asparagus to the dressing and toss to coat evenly.
- ASSEMBLE THE SALAD: Add the crabmeat (breaking it up slightly), shrimp and tarragon to the pasta and toss to combine. Arrange the lettuce on individual plates, top with the pasta salad and serve immediately.