- In a food processor, make pesto by pulsing together tarragon, parsley, garlic, oil, cashews, pecorino, and pepper until coarsely chopped (not minced or paste-like). Set aside.
- To a large pot filled with heavily-salted boiling water, add potatoes, boil until tender, then remove and lay on a sheet tray until cool. To the same water, add haricots verts, boil until crisp-tender, shock in ice water, drain, and let cool.
- Toss potatoes, cannellinis, haricots verts, and pesto together. Season with salt. Garnish with pickled red onions.