Preheat your grill to 350°F to 375°F. If using a 3-burner grill only light 2 sides, leaving 1 off. If you have a 2-burner grill only light 1 side.
Liberally spray a 10-inch cast-iron skillet with cooking spray.
In a small saucepan combine 1 cup chocolate chips and the butter. Cook on low heat, stirring often, until smooth, 3 to 4 minutes (you can do this on the side burner if your grill has one, over the grates on the hot side of the grill or on the stovetop). Remove from the heat and let cool slightly. In a small bowl, whisk together the flour, espresso powder, baking powder, and fine salt.
Pour the melted chocolate into a large bowl, then whisk in the eggs, granulated sugar, brown sugar, and vanilla until smooth. Next, add the flour mixture and stir until you no longer see any flour bits. Add in 1 cup of the remaining chocolate chips and stir to combine.
Pour the batter into the prepared skillet. Top with the remaining 1/2 cup chocolate chips and sprinkle with flaky salt.
Place on the cool side of the grill, close the lid and cook for 20 minutes. Open and turn the skillet a half turn so the other side is closer to the hot side. Close the grill and cook until the brownie is set around the edges, puffed up, and a toothpick inserted in the middle comes out clean, 20 to 25 minutes. Remove and let cool slightly while you grill the berries.
Turn the 2 burners up to high. Lightly spray a grill basket with cooking spray and place on the grill to preheat for 5 minutes. Add the berries and cook just until the berries warm through and some begin to burst, 2 to 3 minutes, shaking the basket often.
To serve, scoop the warm brownie mixture into bowls and top each with a scoop of ice cream and warm berries.