01 -
Preheat the oven to 350°F (175°C). Lightly spray an 8-inch square baking pan with cooking spray.
02 -
In a small bowl, whisk together ½ cup sugar and ¼ cup cocoa powder. Set aside for later use.
03 -
In a large mixing bowl, whisk together the flour, remaining ½ cup sugar, remaining ¼ cup cocoa powder, baking powder, and salt.
04 -
In a medium bowl, whisk together the milk, melted butter, egg yolk, and vanilla extract until smooth.
05 -
Stir the wet ingredients into the dry ingredients until just combined. Fold in the semisweet chocolate chips. The batter will be thick.
06 -
Spread the batter evenly into the prepared baking pan. Sprinkle the reserved cocoa and sugar mixture evenly over the top.
07 -
Gently pour the boiling water over the batter. Do not stir. This allows the sauce to form underneath the cake as it bakes.
08 -
Bake for 22-24 minutes, until the top is cracked, the sauce is bubbling, and a toothpick inserted into the cake comes out mostly clean.
09 -
Let the cake cool on a wire rack for 10 minutes before serving. Serve warm with vanilla ice cream for the best experience.