When summer arrives and the blueberries are so ripe they practically burst at the touch, this is what I make. This is not your nonna’s tiramisù, it is something more sensational. We take those jewel-colored berries and cook them down with lemon and sugar until they surrender all of their deep, dark, glorious juice, and then I bring in the limoncello. Because in my kitchen, the answer to “should I add limoncello?” is always yes. The juice does everything: it soaks the ladyfingers, it turns the mascarpone cream a blushing lilac, and it becomes a glossy, jewel-toned sauce poured dramatically over the top. It’s purple. It’s royal. It’s magnificent. It’s just gorgeous, and it will be the most beautiful thing on your table all summer long.