Betty Crocker is serving its latest cake by the slice, and this time it even comes with a shoulder strap. The century-old baking brand has refreshed the packaging across much of its lineup and marked the occasion with The Betty Ate Collection, three handbags that turn familiar cakes into something to carry rather than cut. The makeover, announced by General Mills, covers Betty Crocker’s cake, brownie, cookie, muffin, and bar mixes, along with its frostings. Boxes are gradually arriving on shelv