Preheat the oven to 350°F. Line a 9 x 13-inch rectangular baking pan with parchment paper on all sides Set aside.
In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, cinnamon, nutmeg, ginger, and salt. Make a well in the center of the dry ingredients and add pumpkin. vegetable oil, eggs, and vanilla extract. Starting from the center of the bowl, whisk outward, pulling the dry ingredients into the middle. Whisk until no streaks of flour remain.
Pour the batter into your prepared pan use a rubber spatula to spread into an even layer. Bake until the cake is risen, the top springs back to the touch, and a butter knife inserted in the center of the cake comes out mostly clean, 30 to 35 minutes. Let the cake cool cool completely before frosting.
Once the cake is cool, make the frosting. Place the egg whites and the sugar in the metal bowl of a stand mixer (or any large heatproof bowl!) and place over a saucepan with a few inches of simmering water in it to make a double boiler.
Whisk the egg whites and sugar together until the sugar is completely dissolved. You can test this by rubbing a little of the mixture between your fingers and making sure you don’t feel any grittiness. If you do, keep whisking the mixture over the double boiler until fully dissolved!
Remove the bowl from the heat and place back on your stand mixer fitted with the whisk attachment and beat on high speed until glossy and stiff peaks forms, about 5 minutes. Add the vanilla extract and a pinch of salt and beat until combined.
Spread the marshmallow frosting over the cooled cake, using the back of a spoon to make big swoops in the frosting. Use a kitchen torch to lightly toast the frosting to your desired toasty-ness! Enjoy!