For the Turkey Casserole Filling

Heat a large skillet with tall sides (my skillet is 12 inches in diameter) over medium heat. Add 3 tablespoons of the butter. Once butter is melted, add the onions, carrots, and celery. Cook for 5 minutes, stirring periodically. Stir in the garlic and cook for another 4 or 5 minutes, or until the vegetables are nicely softened.

Now slide everything in the skillet to one side. Add remaining 2 tablespoons of butter to empty side of skillet. When the butter is melted, sprinkle the flour over the butter, whisking all the while (a flat whisk works great here!). Draw in as much butter and vegetable juices as you can, into the flour. The mixture will be thick. Cook for a minute or two, until the mixture is slightly browned and fragrant.

Slowly pour the chicken broth over the flour mixture, whisking all the while to smooth out the flour. Then slowly pour in the milk, whisking to incorporate until completely smooth. Now bring the entire contents of the skillet together, folding and stirring to incorporate. Stir in dry mustard, Dijon mustard, salt, and pepper. Cook until thickened, about 8 to 10 minutes, stirring occasionally. Then stir in the Parmesan and give the mixture a taste test, adding more salt and pepper if needed. Add the dill, lemon zest and juice, turkey, and peas, and fold to incorporate. Transfer turkey casserole filling to a 9 x 9 inch dish with tall sides, or something of similar size. Level mixture out in the pan.

For the Biscuits

Preheat oven to 375°F.

In a large bowl, whisk together flour, sugar, baking powder, salt, lemon zest, and dill. With a rigid pastry blender or a couple forks, cut the butter into the dry mixture until incorporated and crumbly. Drizzle milk evenly over the top of the mixture and then stir together just until evenly moistened. Do not over mix. Dough will be very thick.

Drop biscuit dough by nine rounded tablespoonfuls onto the turkey casserole filling. Bake, uncovered, for about 35 minutes, or until filling is hot and bubbling and the biscuits are beautifully browned. Let sit for a couple minutes before serving.