Step 1

Arrange a rack in center of oven; preheat to 350°. Drizzle a teaspoon or two of oil into the bottom of 13x9" or 3-qt. shallow baking dish (preferably metal, but glass works too) and use your fingers to rub oil all across bottom, up sides, and into corners to coat all surfaces of pan.

Step 2

Whisk 2½ cups flour, 2 tsp. ground cinnamon, 2 tsp. ground ginger, 1 tsp. baking soda, 1 tsp. salt, and ½ tsp. baking powder in a medium bowl; set aside.

Step 3

Whisk 15 oz. pumpkin purée, 3 eggs, 2 cups brown sugar, ½ cup yogurt, and remaining ½ cup oil in a large bowl until smooth. Pour dry ingredients into pumpkin mixture and whisk just until no floury spots remain and batter is smooth.→ There's only one canned pumpkin puree worth buying...

Step 4

Scrape batter into prepared baking dish with a flexible rubber spatula and spread in an ever layer all the way to the corners. Smooth top.

Step 5

Bake until cake is puffed evenly across the surface, center springs back lightly when pressed, and a cake tester, skewer, or toothpick inserted into the center comes out clean, 25–35 minutes. Let cool.

Step 6

While cake is cooling, slice 10 oz. marshmallows in half. Also carefully raise oven rack so it’s positioned directly underneath broiler. Preheat broiler.→ Wait, what are marshmallows made of, anyway?

Step 7

Arrange marshmallow halves over top of cooled cake (neat rows look cool, but you can be as precise or loose as you like). You might not use the whole bag.

Step 8

Broil cake just until marshmallows are golden and toasted—this literally takes only a few seconds! It will turn to charcoal in an instant, so don’t walk away and keep a very constant, very watchful eye.