Preheat oven to 350 degrees F. With the paddle attachment, combine room temperature butter, brown sugar, and sugar in a stand mixer. (you can also use a hand mixer if you do not have a stand mixer) Beat together on medium until sugar and butter are fully incorporated, about 30 seconds to 1 minute. Scrape down the sides of the bowl as needed.

Add eggs, one at a time, then sweet potato puree, vanilla extract, and . (Mixture may look gritty, however, keep going. Once the flour is added, the batter will become smooth)

Add salt, baking powder, baking soda, and flour. Continue to mix until all dry ingredients are fully incorporated. Scrape down the sides of the bowl and continue to mix for another 10-15 seconds.

Spray an 8x8 baking pan with nonstick baking spray OR line with parchment paper. Add batter and spread evenly throughout pan. Sprinkle top of batter with brown sugar. Bake for 40 minutes.

(if using store bought marshmallow fluff, skip steps 5u00266) While blondies are baking, make the marshmallow fluff. Bring about 1 inch of water to a boil in a sauce pan. In a large bowl, combine egg whites and sugar. Set bowl on top of boiling water and constantly mix together until sugar is dissolved, about 5 minutes. Mixture should be thick and globby.

Add egg white mixture to the bowl of a stand mixer with the whisk attachment and mix on high until a fluff forms - it should be glossy and white. Add cream of tartar and vanilla extract and continue to whisk until stiff peaks form. This will take about 8-10 minutes.

Once blondies are finished, let them cool completely on a cooling rack. Once blondies they have cooled, lather on the marshmallow fluff. Create swirls and char with a torch!