Cover green beans with water in a large pot. Add ham, bouillon, paprika, and cayenne. Bring to a boil over high heat; reduce heat to low and let simmer until beans are tender, about 30 minutes. Remove from heat and let cool, 20 to 30 minutes.

Meanwhile, melt butter in a frying pan over medium heat. Add flour and cook until almost brown, 3 to 5 minutes. Stir in diced onion; cook until it begins to brown, 7 to 8 minutes. Reduce heat to medium-low; cook and stir dried onions in the mixture until they begin to lightly brown, 3 to 4 minutes, being careful as they burn easily. Add paprika and pepper. Pour in water and stir until mixture is smooth.

Whip sour cream in a bowl and mix into flour mixture until smooth. Stir sour cream mixture into cooled green beans. Heat soup over medium heat until simmering; cook until heated through, about 5 minutes. Serve.