Start by adding finely chopped celery, onion, carrots, fresh thyme, sage, salt, and black pepper into a food processor. Pulse until finely chopped, about 15-20 seconds.

In a skillet, heat 2 tablespoons of olive oil over medium heat. Add the finely chopped vegetable mixture and cook for 10-12 minutes, stirring occasionally until softened and fragrant.

In a large mixing bowl, whisk together 2 cups of bread flour, 2 teaspoons of baking powder, 1 teaspoon of baking soda, and 1 teaspoon of granulated sugar. Add a pinch of salt and whisk until combined.

In a separate bowl, whisk together 1 cup of buttermilk and 4 tablespoons of melted unsalted butter until smooth.

Pour the wet mixture into the bowl with the dry ingredients and gently stir until a soft dough forms. Fold in the cooled vegetable mixture.

Preheat your oven to 425°F (220°C) and prepare a baking sheet. Drop heaping spoonfuls of the biscuit dough onto the baking sheet, about 12 mounds.

Bake for 12 minutes, then brush the tops with melted butter mixed with 1 tablespoon of chopped rosemary. Return to the oven for an additional 6-8 minutes until deep golden brown.

Carefully remove the biscuits from the oven and let them cool slightly on a wire rack. Serve warm.