Place the oven rack in the upper third of the oven. Preheat the oven to 425 degrees.
In a 12-by-2 1/4-inch cast iron skillet, melt butter over medium heat. Saute onions until they are slightly golden brown, about 8 to 10 minutes.
Stir in the flour and continue sauteing for another minute.
Slowly add chicken broth and a half and a half while whisking. Add the thyme, rosemary, salt, and pepper to taste.
Cook until it just lightly simmers, stirring constantly, then reduce heat to low so it slightly thickens.
Add the vegetables and chicken and cook about 30 seconds longer (it does not need to be fully heated). Remove from the heat and set aside.
Whisk flour, baking powder, baking soda, and salt together in a large mixing bowl. Make a well in the center of the mixture, and set it aside.
Melt butter in a microwave-safe dish until it is about two-thirds melted. Remove the butter and whisk it in to melt completely (if you melted it all the way, no problem, just let it cool for a few minutes).
Pour butter into buttermilk and whisk until the mixture becomes clumpy.
Using a rubber spatula, fold buttermilk mixture into flour mixture until just combined.
Use a 1/4 cup capacity ice cream scoop (or a greased measuring cup) to scoop out dough and place on prepared pot pie filling in skillet. Repeat this process until all the dough is used up, resulting in 8 biscuits.
Transfer biscuits to the oven and bake until they are cooked through, approximately 17 to 22 minutes, depending on how golden brown you’d like them (keep an eye on them).
Rest for a few minutes before serving. Garnish your Pioneer Woman Chicken Pot Pie With Biscuits with chopped parsley.