Heat 1 teaspoon oil in a Dutch oven over medium-high heat. Add leeks; sauté 6 minutes or until tender and golden brown. Add garlic; sauté 1 minute. Spoon leek mixture into a large bowl.
Place 1/3 cup flour in a shallow bowl or pie plate. Dredge chicken in flour, shaking off excess. Heat remaining 1 tablespoon oil in pan over medium-high heat. Add half of chicken mixture; sprinkle with 1/8 teaspoon salt and 1/8 teaspoon black pepper. Cook 6 minutes, browning on all sides. Add browned chicken to leek mixture. Repeat procedure with remaining chicken mixture, 1/8 teaspoon salt and 1/8 teaspoon black pepper.
Add wine to pan, scraping pan to loosen browned bits. Combine 1 cup broth and 1 tablespoon flour, stirring with a whisk until smooth. Add broth mixture, remaining 2 cups broth, water and mustard to pan; bring to a boil. Stir in chicken and leeks, remaining ¼ teaspoon salt and remaining ¼ teaspoon black pepper. Cover and simmer 30 minutes.
Stir in potato. Cover and simmer for another 30 minutes or until potato is tender. Stir in spinach; cover and simmer 10 minutes. Garnish with crushed red pepper if desired.
Makes six 1½-cup servings.
Originally published in the Richmond Times-Dispatch as Dijon Chicken Stew with Potatoes and Kale in February 2006.