Preheat oven to 350 degrees Line a metal 8-inch square pan with parchment paper, leaving an overhang. Spray with nonstick cooking spray.

In a large microwave-safe bowl combine the chocolate, butter, and oil. Microwave in 30-second bursts, stirring between each burst, until the mixture is completely melted and smooth. Add the sugar to the hot butter mixture and whisk vigorously until combined. Allow to cool until just barely warm.

Add in eggs, yolk, and vanilla extract and whisk for about 1 minute, or until very well combined. This helps create that shiny crust on top.

Use a rubber spatula to stir in the cocoa, flour, espresso powder, and salt until combined. Scrape down the sides of the bowl with a spatula to ensure it’s all evenly combined.

Pour the batter into the prepared baking pan. Bake until a tester comes out with moist crumbs still attached, about 30 minutes. The internal temperature should be 195°Do not overbake.

Let cool completely to room temperature. If they’re still warm from the oven they will be more cakey. Store in an airtight container at room temperature for up to 3 days or in the fridge for up to 1 week.