Preheat a slow cooker to High.

Place a large sauté pan over medium-high heat. Lightly coat the bottom of the pan with olive oil. Cook the fennel and leeks until lightly browned and softened, about five minutes. Stir in the garlic, tomato paste, wine, and raisins and continue cooking for one minute more.

Transfer the mixture to the slow cooker insert. Cover and cook on High for three hours.

To clean the fresh artichokes, use a paring knife to cut the outside leaves free from the body of the vegetable. Continue turning your knife around the artichoke until you have an equal amount of green leaves with yellow tops. Leave the stem intact—it gives the artichoke a pretty shape. If you like, peel some of the tough green fibers from the outside of the stem with a paring knife. Cut the artichoke in half lengthwise and scoop out the choke (if any) with a melon baller. Place the artichoke pieces in a bowl of cold water with the lemon juice to keep the artichokes from turning dark.

Add the pine nuts, artichokes, mint, parsley, and thyme to the vegetable mixture. Add salt and pepper to taste. Cover and cook on High for one hour more.

Serve the caponata warm or cold. Drizzle with additional olive oil, and garnish with fennel fronds or chopped mint, if desired.