Preheat oven to 350 °F (175 °C) and line an 8×8-inch square baking pan with parchment paper.

In a small pot over low heat, melt together the chocolate chips and olive oil until smooth, then set aside to cool slightly.

In a large bowl, whisk eggs, sugar, and vanilla until combined.

Mix in cacao powder, arrowroot powder, espresso powder, baking powder, and salt until incorporated.

Add the melted chocolate mixture and stir until smooth.

Transfer batter to prepared pan and smooth the top evenly.

Bake for 22–25 minutes or until a toothpick inserted in the center comes out clean.

Let brownies set in the pan for 15 minutes, then transfer to a wire rack and cool completely (1–2 hours) before frosting.

For frosting, beat heavy cream and mascarpone until combined, about 30 seconds.

Add powdered sugar and vanilla and beat for 1–2 minutes until thickened.

Spread frosting evenly over cooled brownies and dust with cacao powder.

Slice and serve.