1. Prep ingredients
Preheat oven to 350℉ with a rack in the center. Halve leek lengthwise, rinse under running water to remove any grit, and pat dry. Cut half of the leek crosswise into ¼-inch pieces (save remaining half for own use). Halve pepper, discard stem and seeds, then cut into ¼-inch pieces. Pat chicken dry and season all over with salt and pepper.
2. Sear chicken
Heat 1 tablespoon oil in a medium skillet over high until shimmering. Add chicken in a single layer and cook, undisturbed, until browned on the bottom but not cooked through, 2–3 minutes. Transfer chicken to a plate and set aside until step 5 (chicken will finish cooking later).
3. Cook vegetables
Melt 3 tablespoons butter in same skillet over medium-high heat. Add chopped leeks, peppers, and a pinch of salt. Cook, stirring occasionally, until vegetables are softened, translucent, and tender, 7–10 minutes. (Reduce heat if vegetables are starting to brown before they are tender.)
4. Bloom aromatics
To skillet with vegetables, stir in 2 teaspoons each of paprika, tomato paste, and flour. Cook over medium-low heat, stirring often, until paprika is fragrant and tomato paste is darkened slightly, about 2 minutes.
5. Simmer chicken paprikash
Toast baguette directly on center oven rack until warm and crusty, about 5 minutes. Stir chicken broth into skillet with vegetables. Bring to a boil. Simmer over medium heat until liquid is slightly thickened and flavorful, 3–4 minutes. Stir in browned chicken and peas; simmer chicken is cooked through, and peas are warm, about 2 minutes.
6. Finish & serve
Pick a few dill fronds for garnish, then finely chop remaining fronds and stems. To skillet with chicken paprikash, stir in chopped dill, all of the sour cream, and ¼ teaspoon vinegar. Season to taste with salt and pepper to taste. Spoon paprikash into bowls and garnish with picked dill fronds. Serve with warm bread on the side. Enjoy!