Instructions

1. For the frosting: combine sugar, flour, and salt in a medium-sized saucepan and whisk well to combine and remove any lumps from the flour.
2. Turn stovetop heat to medium and whisk in milk until mixture is smooth. Continue whisking constantly until mixture is thickened to a pudding-like consistency (do not crank up the heat or you’ll burn it and the sugar won’t dissolve properly) and the whisk leaves a trail.
3. Remove from heat and pour into a heat-proof container and cover the surface with a piece of plastic wrap, wax paper, or parchment paper pressed directly against the surface (to prevent a skin from forming). Allow to cool completely to room temperature (alternatively you may make this mixture a day or two in advance, store in the refrigerator, then bring to room temperature before proceeding). We’ll come back to this in step 9.
4. For the brownies, start by caramelizing your white chocolate. Preheat the oven to 250 F. Place your white chocolate, broken up into pieces or coarsely chopped, onto a baking sheet or 9×13 pan lined with parchment paper. Put the chocolate in the oven for about 40-45 minutes, and every 10 minutes, take it out and stir it around/smooth it with a spatula, so that it browns evenly. After 40 minutes in the oven, the chocolate will have taken on a golden, light brown color. Since we need our chocolate to be melted, it’s ready to use immediately in the recipe!
5. Preheat the oven to 350°F and grease a 9×13-inch baking pan or line with aluminum foil or parchment paper, leaving an overhang on the sides to lift the finished brownies out (makes cutting easier!). Set aside.
6. In a microwave-safe bowl, melt the butter. Then, add in your still-melty caramelized white chocolate. Whisk together until completely smooth. Whisk in the sugar until completely combined, then whisk in the eggs and vanilla. Whisk in the flour and salt. Batter will be thick. Spread evenly into prepared pan.
7. Bake for 30 minutes, covering loosely with aluminum foil halfway through. Test the brownies with a toothpick at the 30 minute mark. Insert it into the center of the pan. If it comes out with wet batter, the brownies are not done. If there are only a few moist crumbs, the brownies are done. Keep checking every 2 minutes until you have moist crumbs. My brownies take 32 minutes.
8. Remove from the oven and place on a wire rack to cool completely before frosting.
9. To finish the frosting: Once flour mixture has cooled, use an electric mixer or stand mixer to beat butter on high speed until it is light and fluffy (this usually takes several minutes, and you may need to scrape the bowl with a spatula).
10. Reduce mixer speed to medium and gradually add flour mixture, one heaping spoonful at a time, waiting until each spoonful is incorporated before adding the next and beating until all ingredients are well-combined. Scrape sides and bottom of bowl with a spatula, then stir in vanilla extract.
11. Gradually increase speed to medium-high and whip frosting until it is smooth, light, and airy (it should not seem greasy). If you have any difficulty or experience your frosting splitting please see the troubleshooting section in the blog post.
12. Use your spatula to deflate the frosting to work out any air bubbles, then use as desired.
13. Cover and store leftover frosted brownies in the refrigerator for up to 1 week, or if the brownies are not frosted, at room temperature for up to 1 week.