Preheat your oven to 180 C / 350 F
Butter and flour a 8 inch square cake pan . You can line the bottom with parchment (optional)
In a bowl , whisk together flour , baking powder and salt. Keep aside.
In a saucepan , heat together butter and milk until butter melts . Keep this warm until needed
In a large bowl , beat together the eggs , sugar and vanilla
Beat well until mixture is tripled in volume and is light and fluffy.
Beat or fold in the flour mixture at low speed until all the flour is mixed in. Scrape the sides and bottom of bowl to make sure.
Beat in the hot milk-butter mixture until smooth. This will take only a few seconds
Pour batter immediately into prepared pan and bake for 20 to 25 minutes until top is set , springs back when pressed and maybe even lightly browned
As the cake bakes, make the topping.
In a saucepan , heat together brown sugar , milk and butter until melted and bubbling .
Take off heat and stir in the coconut.
Once the cake has baked for 20 to 25 mins , take out from oven and increase the temperature to 200 c / 400 F.
Spread the topping on the cake as evenly as possible
Return to oven and bake for 10 minutes until the top is well browned
Cool in pan for 10 minutes and gently remove .
Cool completely on wire rack