Take advantage of rhubarb season with this easy dessert. Baked and unmolded, this cake resembles a pale pink mosaic atop velvet-crumbed and vanilla-infused cake. The rhubarb, which you’ll add in raw, is tangy and tender, firm enough to give you something to chew over. It’s an easy half-hour of prep and another hour and change in the oven, ample time for a light supper, anticipation of dessert hanging in the spring air.