In a medium-sized saucepan whisk the ¼ cup granulated white sugar, 3 tablespoons cornstarch, and ⅛ teaspoon kosher salt together. Add the 4 egg yolks and whisk until smooth. Finally, whisk in the 2 cups whole milk.
Cook over medium-high heat whisking constantly, until the custard begins to thicken. Once it begins to thicken, continue whisking stopping occasionally to check for bubbles.
Once the custard begins to bubble continue cooking and whisking for 1 minute.
Remove the saucepan from the heat and whisk in the 2 tablespoons unsalted butter and 1 tablespoon vanilla extract.
Pour the custard over the brownie and smooth it into an even layer.
Cover with foil or plastic wrap to keep the surface of the custard from drying out and chill in the refrigerator for at least four hours and up to four days.
When ready to serve, remove the covering and use a paring knife to slice around the edges to keep the custard from sticking. Remove the brownies from the pan using the parchment paper sling. Cut into individual servings and place each brownie on a plate.
Sprinkle the tops evenly with 1 teaspoon of granulated white sugar.
Ignite your torch and hold the flame about 4 inches from the surface of the custard. Using a circular motion heat the sugar until it browns and forms a crust.
The longer you brulee the sugar, the darker, more caramelized, and bitter it will become. The bitterness contrasts nicely with the sweetness of the custard and brownie.