Melt the butter in a Dutch oven on medium heat. Add onions, celery and thyme and stir to combine. Cook for 8 to 10 minutes, until the veggies are softened.
Add flour to the Dutch oven and stir constantly for 1 minute.
Add chicken broth, potatoes, salt and pepper. Stir to combine. Bring to a boil on high heat and then reduce heat to medium and cover. Cook for 10 minutes, stirring every few minutes.
Add sardines, scallops, shrimp, and clams and stir together. Cook another 20 minutes on medium heat, uncovered.
Stir in the whipping cream and capers. Cook for 3 to 5 minutes. Garnish with fresh parsley, if desired. Serve hot.