Preheat oven to 350°F. Grease and flour an 8-inch square baking pan.
Brown Sugar Cake:
Beat milk, corn syrup, egg and vanilla in a small bowl; set aside. Mix flour, baking powder, baking soda and salt in a large mixer bowl. Add sugar and brown sugar; mix on low speed to combine. Add butter, one piece at a time, mixing on low speed about 45 seconds, until butter and flour begin to clump together. With mixer still running, add two thirds of egg mixture. Increase speed to medium-high; beat 1 minute until light and fluffy. Gradually add remaining egg mixture. Scrape sides and bottom of bowl. Beat again on medium-high until thoroughly combined, about 15 seconds. Spread batter in prepared pan.
Bake 30 to 35 minutes until cake is golden brown and toothpick inserted in center comes out clean. Prepare Caramel Nut Topping while cake is baking.
Caramel Nut Topping:
Combine brown sugar, flour and salt in a small bowl. Stir in corn syrup, evaporated milk, butter and nuts or coconut.
When cake is finished baking, remove from oven. Set oven temperature to 400°F. Carefully spread Caramel Nut Topping over hot cake, a small amount at a time. Bake 7 to 10 minutes or until entire surface of topping is bubbly. Cool slightly. Cut cake in pan and serve warm.