Preheat the oven to 350°F.
Mix 3 cups of the flour with the white sugar, baking soda, salt, eggs, 2 teaspoons of the vanilla, and the milk.
Stir in the melted butter gradually, then pour the batter into a greased 13x9-inch baking dish.
Now combine the 2 sticks of room temperature butter with the brown sugar, cinnamon, nuts, and 2 tablespoons of the flour in another bowl.
Once well combined, drop tablespoons of the Cinnamon and nut mixture over the cake batter in the baking dish.
Use a sharp knife to swirl it throughout the cake.
Bake for 25 minutes or until a toothpick inserted into the middle comes out almost clean and the cake is pulling away from the pan edges a bit.
Whisk the milk, powdered sugar and vanilla until smooth.
Drizzle it over the cake while still warm.