Stir beans, stock concentrate, smoked paprika, ¼ cup water (⅓ cup for 4 servings), and a large pinch of salt and pepper into pot with veggies. Bring mixture to a low simmer, then reduce heat to low. Cook until thickened, 7-8 minutes. Turn off heat; stir in 1 TBSP butter and season with salt and pepper. Cover to keep warm.