To make the seasoning blend, place bouillon powder, black pepper, onion powder, garlic powder, and salt in a small bowl, stir to combine, and set aside.
Sandwich the chicken breasts in between sheets of wax paper or plastic wrap.
Pound the chicken using a meat mallet into thinner cutlets.
Season the chicken cutlets with 2 teaspoons of the seasoning blend.
Place flour, baking powder, baking soda, and 2 teaspoons of the seasoning blend into a shallow bowl. Whisk to combine.
Place the buttermilk and egg in another shallow bowl, season with 2 teaspoons of the seasoning blend, and whisk to combine.
Spoon schmaltz into a large skillet and melt over medium-high heat until the temperature reaches 325 F to 350 F.
While the schmaltz is heating, coat the chicken in the seasoned flour, shaking off any excess.
Next, dip the chicken into the buttermilk mixture, letting any excess drip off.
Return the chicken to the flour and coat. Use your hands to press and adhere the flour to the cutlet.
Working in batches, carefully place the chicken into the hot schmaltz, and fry for 3 to 4 minutes per side or until crisp and cooked through.
Remove the fried cutlets from the skillet and set aside on a wire rack to rest and drain.
Carefully remove ¼ cup of the hot schmaltz from the skillet and transfer to a small saucepan.
Add ⅓ cup of flour to the pan and whisk to combine the roux. Cook the roux over medium heat for 1 minute.
Add the milk and the remaining seasoning (about 1 teaspoon) to the saucepan and whisk to combine with the roux. Bring to a simmer and cook for 3 to 4 minutes, or until the gravy has thickened.
Divide the chicken between plates and top with gravy before serving.