For the Brownies:
¾ cup all-purpose flour
1 teaspoon baking powder
½ teaspoon salt
½ cup unsalted butter
3 ounces unsweetened chocolate
½ cup granulated sugar
½ cup light brown sugar
1 egg yolk
1 teaspoon vanilla extract
½ cup semisweet chocolate chips
For the Frosting:
6 tablespoons unsalted butter, at room temperature
¼ cup unsweetened cocoa powder
¼ teaspoon salt
1¼ cups powdered sugar
1 tablespoon milk
½ teaspoon vanilla extract
¼ cup heavy cream
3 tablespoons Ovaltine chocolate malt powder
1. Make the Brownies: Preheat oven to 350 degrees F. Butter an 8-inch-square baking dish and line with parchment paper, letting the excess hang over the edges. Butter the parchment paper; set aside.
2. In a small bowl, whisk together the flour, baking powder, and salt; set aside.
3. Bring about an inch of water to a simmer in a medium saucepan. Place a medium, heatproof bowl on top of the saucepan (do not let it touch the water) and add the butter and unsweetened chocolate. Stir occasionally, until the chocolate and butter are completely melted and smooth. Remove the bowl from the saucepan and whisk in the granulated and brown sugars. Whisk in the egg, the yolk, and the vanilla extract. Add the flour mixture all at once, and fold it into the chocolate mixture with a rubber spatula until combined. Fold in the chocolate chips.
4. Pour the batter into the prepared pan and bake for 25 to 30 minutes, or until a thin knife inserted in the center comes out clean. Allow to cool completely; meanwhile, make the frosting.
5. To Make the Frosting: Using an electric mixer, cream together the butter, cocoa powder, and salt on medium speed for about 3 minutes (mixture will be thick).
6. Scrape down the sides of the bowl and add the powdered sugar. Mix on low speed to incorporate the sugar, and while the mixer is running, slowly add the milk and vanilla extract. Gradually increase the mixer speed to medium-high, beating until smooth, scraping the sides of the bowl as necessary.
7. In a 1-cup measuring cup, or in a small bowl, mix together the cream and the Ovaltine. Reduce the mixer speed to medium, and pour the cream mixture in a slow, steady stream and mix until thoroughly combined. You can add more powdered sugar a tablespoon at a time, if you would like a stiffer frosting.
8. Spread the frosting onto the cooled brownies, and cut into squares. Store brownies in an airtight container, or tightly wrapped, at room temperature for up to 5 days.