To prepare sauce, combine first 6 ingredients in a bowl, stirring well. Cover and chill.
To prepare cakes, heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add leek to pan; sauté 3 minutes or until tender. Place leek in a large bowl. Wipe pan with paper towels.
Place potato in a sieve; gently squeeze potato to remove excess moisture. Add potato, flour, 1/2 teaspoon salt, 1/2 teaspoon pepper, and eggs to leek in bowl; stir well. Return pan to medium-high heat. Recoat pan with cooking spray. Divide potato mixture into 16 equal portions, shaping each into a 1/4-inch-thick patty. Add 8 patties to pan; cook 5 minutes on each side or until golden. Repeat procedure with remaining 8 patties. Serve with sauce.