How to Make It
In a saucepan of boiling salted water, cook the yellow beans until just tender, 3 minutes. Using a slotted spoon, transfer the beans to a baking sheet and let cool. Add the green beans to the boiling water and cook until just tender, 2 minutes. Using the slotted spoon, add the green beans to the baking sheet. Let cool, then pat dry.
Add the garlic, bay leaves, thyme, rosemary and peppercorns to the boiling water. Add the potatoes and simmer over moderately high heat until tender, about 20 minutes. Drain the potatoes, reserving the garlic cloves. Discard the seasonings.
Meanwhile, in a small bowl, soak the anchovies in the milk for 10 minutes. Drain the anchovies, then coarsely chop them and transfer to a blender. Add the olive oil and the reserved garlic and puree. With the machine on, slowly add the vinegar. Scrape the dressing into a bowl, season with salt and pepper and stir in the parsley and marjoram.
Slice the boiled potatoes 1/4 inch thick and put them in a large bowl. Add half of the anchovy dressing and toss gently. Add the yellow and green beans, the cherry tomatoes and the remaining dressing, toss gently and serve.