Preheat oven to 350 degrees F (175 degrees C). Generously grease a 9x13-inch baking dish.
Bring water, brown sugar, and 1/4 cup butter to a boil in saucepan until the sugar dissolves and the mixture is syrup-like; reduce heat to low and keep warm.
Beat 2 tablespoons butter and white sugar together with an electric mixer in a large bowl until smooth.
Sift flour, baking soda, salt, nutmeg, and cinnamon together in a separate bowl; add gradually to the butter mixture alternately with the milk, beating to integrate each addition before adding the next until you have a moist batter. Fold raisins and walnuts into the batter; pour into prepared baking dish. Drizzle the syrup over the batter.
Bake in preheated oven until firm, 40 to 45 minutes.