Place raisins, sugar, butter, slightly beaten eggs, milk, and vanilla in a large heavy-bottomed saucepan and cook over medium heat, stirring frequently, until mixture is hot, slightly thickened, and just beginning to bubble. Cool slightly, uncovered, in the refrigerator. Stir flour with baking powder, baking soda, and salt in a large mixing bowl. Make a well in center, and pour in warm raisin mixture; stir just until combined. Stir in nuts until evenly mixed. Spoon batter into greased muffin cups. Bake in center of oven at 350 degrees until golden, about 15 to 17 minutes. Remove from oven, and immediately pour about 1 tsp. syrup over each tart. Cool tarts in pan for 10 minutes, then remove to a rack and serve warm.