Preheat oven to 350 degrees. Line a 9×13 baking dish with parchment paper, spray with baking spray, and set aside.
Mix the milk, eggs, vanilla extract, and sugar in a medium mixing bowl.
In a separate bowl, sift together the flour, salt, and baking powder.
Gradually mix the flour mixture into the egg mixture. Pour batter into prepared baking pan.
In a bowl, mix together all the topping ingredients, until small pebbles form. Sprinkle the pebbles over the top of the batter.
Bake in oven for 30-35 minutes. Remove from oven and place on a cooling rack.
In a small bowl, mix the powdered sugar, milk, and vanilla extract. Add milk in 1/2 teaspoon increments until icing is liquidy and pourable. After coffee cake has cooled, pour the icing evenly over the top of the coffee cake.