Preheat oven to 450 degrees. Place heirloom tomato slices on several layers of paper towels. Top with a single layer of paper towels. Let stand 15 minutes. Combine 1 cup water, garlic, leek and quartered tomato in a medium saucepan; bring to a boil. Reduce heat; simmer 10 minutes. Strain through a sieve over a bowl, pressing to extract liquid; discard solids. Pour liquid into pan; stir in 1/2 teaspoon salt and 1/4 teaspoon pepper. Cool to room temperature. Sprinkle with gelatin; let stand 5 minutes. Bring gelatin mixture to a boil; boil 3 minutes. Remove from heat. Lightly brush eggplant slices with oil; arrange in a single layer on a baking sheet coated with parchment paper. Bake at 450 degrees for 10 minutes; turn and bake an additional 5 minutes or until tender. Lightly coat a 9 X 5 inch loaf pan with cooking spray. Line pan with plastic wrap. Arrange tomato slices in a double layer on bottom of pan; sprinkle with remaining 1/4 teaspoon salt and 1/4 teaspoon pepper. Top tomatoes with a thin layer of cheese; sprinkle with 1 1/2 teaspoons thyme and 1 1/2 teaspoons chives. Arrange 3 eggplant slices over cheese. Repeat layers, ending with tomatoes. Pour gelatin mixture over terrine. Cover with plastic wrap. Chill 8 hours or overnight. Turn terrine out onto a platter. Let stand 1 hour (or until room temperature).