For the Chicken: Combine ingredients a 5-quart pot. Cover and place over medium-high heat until stock registers about 150°F.. Lower heat to maintain temp until thickest part of chicken 135°F, about 1 hour. Remove with tongs, set aside and cover loosely. Strain stock through a mesh sieve into a large bowl, discard solids, and set stock aside to cool

For the Filling: Combine gelatin and 1/4 cup cooled stock in a small bowl and whisk until smooth; set aside. In 5-quart saucier, melt butter then whisk in flour fragrant and a nutty blond color, about 5 minutes. Add white wine and 1 quart reserved stock, stirring constantly until smooth. Stir in diced onion, carrots, and celery and continue cooking and stirring until vegetables are slightly softened, about 7 minutes more. Increase heat and bring to a boil, stirring constantly. Once it begins to bubble, remove from heat.

Off heat, stir in prepared gelatin has fully melted into sauce. Add frozen peas, diced pimentos, salt, thyme, pepper, and Worcestershire.

Dice chicken then stir into filling. (Filling can be covered and refrigerated up to 3 days.) Divide filling among 6 oven-safe dishes, or use 2-quart glass or ceramic baking dish (approximately 7x11). Place on a foil-lined baking sheet and set aside.

For Biscuit Topping: Preheat oven to 400°F. In a medium bowl, whisk together flour, sugar, baking powder, and salt. Add butter and toss to break up the pieces, then smash each one flat between your fingertips until butter is broken up, like cereal flakes. Stir in buttermilk with a flexible spatula, then drop the thick dough in 1-tablespoon portions over filling.

Bake until biscuits are golden and filling is bubbling, about 45 mins to 1 hour, longer if filling has been chilled. Cool at least 30 minutes before serving to allow the filling to thicken.