In a large bowl, whisk together the flour, baking powder, and 1/2 teaspoon of the kosher salt until evenly combined.

Add the Greek yogurt and 2 tablespoons olive oil. Stir with a wooden spoon until a shaggy dough forms, then turn out onto a lightly floured surface and knead just until smooth, about 1 minute. The dough should feel tacky but not sticky - add a sprinkle more flour if needed.

Preheat oven to 450°F with a rack in the center position. Divide dough into 2 equal pieces. On parchment paper, press or roll each piece into an irregular oval about 1/4 inch thick - don't worry about perfect shapes, rustic is better here.

In a small bowl, combine the melted butter, grated garlic, rosemary, thyme, and remaining 1/4 teaspoon kosher salt. Brush this mixture generously over both flatbreads, getting right to the edges.

Transfer flatbreads on their parchment to the baking sheet. Bake 10-12 minutes, rotating the pan halfway through, until the edges are deep golden and crisp with some darker spots. The centers should still have a little give when pressed.

Immediately brush with any remaining garlic-herb butter from the bowl and sprinkle with flaky sea salt. Cut into wedges or rustic pieces and serve warm.