Preheat the oven to 425°F and line a baking sheet with parchment paper.
Place the chicken breast in a shallow dish and pour 1/4 cup of buttermilk over it to marinate, seasoning lightly with salt, pepper, and a pinch of dried rosemary. Let it sit for at least 15 minutes.
In a separate bowl, combine the whole wheat flour, baking powder, remaining dried rosemary, and a pinch of salt and pepper.
Remove the chicken from the marinade, then dredge it in the flour mixture, shaking off any excess for a light, crispy coating.
Place the coated chicken on the prepared baking sheet and drizzle a little melted unsalted butter over the top.
Bake the chicken for about 20-25 minutes or until the internal temperature reaches 165°F and the coating is crispy.
Meanwhile, prepare the herb-buttermilk biscuit dough by mixing the remaining 1/4 cup buttermilk with the flour mixture, adding the melted butter, a pinch of salt, and stirring until just combined. Drop spoonfuls of the dough onto a separate small baking sheet.
Bake the biscuits in the same oven for 12-15 minutes until they are golden and cooked through.
Remove both the chicken and biscuits from the oven and serve immediately while warm.