Stir together the buttermilk, Dijon, paprika, cayenne and salt in a large bowl. Add the chicken pieces and submerge them to coat. Allow to sit for at least 30 minutes but ideally as long as possible (up to 2 hours at room temperature or up to 8 hours refrigerated).
Preheat the oven to 375 degrees F; set a rack in a rimmed baking sheet.
Combine the flour, salt, baking soda and mustard powder in a bowl. Remove the chicken from the soak mixture and add to the flour mixture, turning to coat. Remove, dip again in the soak mixture and then again in the flour mixture.
Heat 1 1/2 inches of oil in a very large cast-iron skillet over medium-high heat. When hot, shallow-fry the chicken, turning once, until golden brown and an instant-read thermometer inserted into the thickest part (avoid the bone) registers 165 degrees F, around 15 minutes per side. Transfer the chicken to the prepared baking sheet and place in the oven to finish cooking through, if necessary.
Serve fired chicken with plum cornbread and bacon green beans.
Preheat the oven to 350 degrees F. Butter an 8-inch cast-iron skillet or an 8- by 8-inch square baking pan.
Combine the flour, cornmeal, baking powder and salt in a large mixing bowl. Combine the milk, honey, vanilla and eggs in another mixing bowl and whisk to thoroughly combine. Just before combining the wet and dry ingredients, whisk in the melted butter into the wet mixture. Make a well in the dry ingredients and pour the wet ingredients into the well. Mix gently to combine. When the mixture has just come together, transfer it to the prepared skillet or baking pan. Sprinkle the plums in an even layer over the top of the batter. Bake for 25 to 30 minutes. Remove from the oven and let cool before cutting.
Blanched Green Beans with Bacon:
Bring a stock pot of salted water to a boil. Add the green beans and cook for 2 to 3 minutes. Prepare a bowl of ice water and shock the beans to stop the cooking process. Add the oil and bacon to a saute pan over medium-high heat. Let the bacon cook until its crunchy. Mix in the green beans and toss to coat with the bacon.