Grease Sweetie Pie with some butter. On a floured surface, roll both dough discs into a circle approximately 12 inches in diameter. Fit one into Sweetie Pie, lay the other on top, and refrigerate.
In Deep Cut, melt 2 tablespoons of butter over medium-low heat; add red onions, and sauté 15 minutes or until caramel-colored. Place onions in a bowl and set aside.
In the same pan (Deep Cut), fry bacon until crispy. Drain on a paper towel. Chop when cooled. Reserve 2 tablespoons bacon grease.
Preheat oven to 375 degrees Fahrenheit and position an oven rack to the middle position.
Combine all-purpose flour, salt, and pepper in a large bowl; dredge chicken tenderloin pieces in flour mixture.
Whisk together chicken broth, milk, and mustard in a bowl. In the same pan used for the bacon, melt the remaining 2 tablespoons butter with the reserved bacon grease over medium-high heat. Add chicken tenderloins, and brown on all sides until golden.
Sprinkle the remaining flour mixture on top of chicken pieces, then gradually stir in the chicken broth mixture.
Bring to a simmer and cook, constantly stirring, until thickened, about 5 minutes. Add red onion and torn escarole, stir to incorporate, and cook for one more minute.
Remove from heat and allow the filling to cool for 10 minutes, occasionally stirring, before spooning into prepared pie shell.
Top with crust circle and crimp as desired. Cut steam vents and brush the top of the pastry with milk.
Bake for 1 hour. Cool before slicing.
Photos by Adam Friedlander.