Heat the oven to 350°F (177°C). Lightly butter a 10-ounce ramekin and set aside.
Place 2 tablespoons of butter in a small microwave-safe bowl and microwave until melted. Set aside to cool slightly.
In a small bowl, whisk together the sugar, flour, and cocoa powder.
Stir in the melted butter, egg yolk, and vanilla just until combined. Do not overmix.
Gently fold in the chocolate chips and 2 crumbled Oreo cookies.
Pour the batter into the prepared ramekin and spread evenly. Top with remaining chocolate chips and 1 crumbled Oreo. Bake for 30 minutes.
Remove from the oven and let cool for 5 minutes before serving.
Notes
Use Quality Chocolate: Well-known brands like Ghirardelli, Guittard, or Scharffen Berger deliver better flavor. Trader Joe’s and Whole Foods 365 are reliable, budget-friendly options.
Use the Right Ramekin: A 10-ounce ramekin gives the best texture and bake time. Smaller or larger dishes can affect how the brownie bakes.
Do Not Overmix: Stir just until the batter comes together. Overmixing can make the brownie more cake-like instead of fudgy.
Watch the Bake Time: Bake just until set. Overbaking leads to a dry brownie, and it will continue to firm up as it cools.