Preheat the oven to 400 degrees . Line a 12-cup muffin pan with 1 1/4-inch paper liners. In a bowl, whisk the flour, baking powder, 1/2 cup Gruyere, Parmesan, 1 tbsp. thyme, tarragon, chives and salt. In a large bowl, whisk the buttermilk, oil and eggs. Add the dry ingredients to the wet mixture and fold until just barely blended.
Divide the batter among the liners (fill about three-quarters); top with 1/2 tbsp. Gruyere and pinch of chopped fresh thyme. Bake until puffed and golden brown and a toothpick inserted into the center comes out clean, 13 to 17 minutes. Cool in the pan.