How to Make It
On a cutting board, mash the garlic with the salt to a paste. Add the anchovies and mash to a paste. Scrape the paste into a bowl and stir in the mayonnaise, olives, lemon zest and lemon juice. Gradually whisk in the olive oil. Cover the aioli with plastic wrap and refrigerate until chilled.
Meanwhile, fill a large bowl with ice water. Bring a large pot filled with 1 inch of salted water to a rolling boil. Spread the beans in a steamer basket and steam just until crisp-tender and the color is still vibrant, especially the purple beans (which turn green when fully cooked), 1 to 2 minutes. Immediately plunge the beans into the ice water to stop them from cooking further; let cool completely. Drain the beans and pat them dry. Transfer the beans to a platter and serve with the aioli.