Dice the onion and add it to a deep, oven safe skillet with 3 Tbsp butter. Sauté the onions over medium heat until soft and transparent. Add 3 Tbsp flour and continue to sauté for about two minutes. Whisk in one cup milk until no lumps remain. Add the salt, thyme, sage, and some freshly cracked pepper. Allow the milk to come up to a simmer, whisking often, until it thickens.

Whisk in the vegetable broth and allow it to come up to a simmer again. You should now have a thick, creamy sauce. Add the frozen vegetables (no need to thaw) and stir to combine. Turn the heat down to low and allow the mixture to heat through, stirring occasionally, while you prepare the biscuit topping.

Preheat the oven to 425ºF. In a large bowl stir together the flour, baking powder, and salt until well combined. Cut the butter into several chunks, add it to the flour mixture, then use your hands or a pastry cutter to work the butter into the flour until the mixture resembles damp sand. Stir in the cheddar and chives.

Add 1 cup milk to the biscuit mixture and stir until a dough forms. If the dough seems is too wet or sticky to work with your hands, simply dust a little more flour on top.

Turn the dough out onto a lightly floured surface and press it down into a 3/4-inch thick circle, then cut into 6 biscuits (gather up the scraps and reshape to cut more biscuits if needed). Place the biscuits over top of the vegetable pot pie mixture in the skillet.

Bake the skillet for 18-20 minutes, or until the biscuits are golden brown on top and the filling is bubbly around the edges. Serve hot.