Walnut-Lentil Patties

2 1/2 cups cooked lentils, drained (1 cup raw)
2 cups walnuts, finely chopped
2 cups fresh bread crumbs
2 eggs, lightly beaten
1 onion, finely chopped
2 tablespoons catsup
1/4 teaspoon ground cloves
1/2 teaspoon salt
1/4 teaspoon pepper
Dairy sour cream (if needed)
2 tablespoons vegetable oil
2 tablespoons butter

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