Preheat oven to 400°. In a large bowl, combine flour, 1/2 cup sugar, baking powder, cinnamon, and salt. In another bowl, whisk together milk, butter, egg, vanilla, and coffee granules until blended. Add to flour mixture along with strained raisins and walnuts. Mix with a spatula until just blended, taking care not to overmix.
Spoon batter into 12 paper-lined muffin cups. Sprinkle with remaining 3 Tbsp. sugar. Bake until a toothpick inserted into center of a muffin comes out clean, 20 to 25 minutes. Serve warm straight from pan.