Start by preheating your oven to 425°F so it's fully hot by the time your flatbread is assembled. A hot oven is what gives you that crisp base instead of a soggy one. Line a baking sheet with parchment paper while you wait.
Lightly flour your work surface and roll or stretch the dough into an oval or rectangle, about 1/4 inch thick. I like to leave the edges slightly thicker so they puff up into a nice crust. Transfer it onto the prepared baking sheet.
Brush the entire surface of the dough with half of the olive oil. This step matters more than it seems, since it stops the toppings from making the dough soggy while it bakes. It also helps the edges turn golden brown.
In a small bowl, toss the halved grapes with the remaining olive oil, a pinch of salt, and black pepper. This quick step coats them evenly so they caramelize instead of just steaming in the oven.
Scatter the torn brie pieces evenly across the dough, then top with the seasoned grapes. Don't overcrowd the flatbread, since the toppings need a little breathing room to roast properly instead of turning mushy.
Slide the tray into the oven and bake for 18 to 20 minutes, until the crust is golden, the brie is fully melted, and the grapes look slightly blistered. Keep an eye on it after the 15-minute mark since ovens vary.
Pull the flatbread out and immediately sprinkle it with fresh rosemary and flaky sea salt. If you're using honey, drizzle it on now while everything is still warm so it melts slightly into the cheese. Slice and serve right away.