Nastassia Johnson, blogger behind Let Me Eat Cake, has picked out several items to try at downtown’s Semi Sweet Bakery on a recent afternoon: a croissant flecked with chocolate, an Almond Joy doughnut, and a cookie called “Triple Chip” — chocolate, butterscotch and potato. She wanted a slice of 7-Up Pound Cake, too, but another customer nabbed the last one. Johnson samples baked sweets all over L.A., and shares discoveries on her blog. (And Instagram, too.) She also posts recipes from her own baking experiments — buttermilk spiced doughnut-muffins one day; ginger aprium muffins another. Also cheesecake infused with ube (a purple yam used in Filipino cooking) in a nod to her Filipino heritage….