Preheat oven to 350ºF. Grease an 8-inch square baking pan.
In a medium bowl, whisk together flour, baking powder and salt.
In a large bowl, whisk melted butter, sugar, egg, egg yolk and vanilla until smooth.
Stir in pineapple until well combined. Stir in flour mixture just until combined.
Transfer batter to prepared baking pan. Bake until top is golden brown and toothpick inserted into center of cake comes out clean, about 20-25 minutes.
Topping
In a medium saucepan over medium heat, melt butter with sugar, brown sugar and salt. Whisk in heavy cream.
When mixture starts to bubble, turn heat down to low and simmer until thickened, about 3 minutes.
Remove from heat and stir in coconut, pecans and vanilla. Spread over warm cake. Let cool at least 15 minutes before cutting cake.