Preheat oven to 350 degrees.
Coat a 9.5 x 13.5 x 2 inch deep glass baking dish with baking spray; set aside.
In a large mixing bowl, add all flours and baking powder. Whisk to combine; set aside.
In another medium bowl, whisk sugar and eggs until creamy. Add the purple yam, melted butter, coconut milk, evaporated milk, and purple yam extract. Whisk until well incorporated.
Add the egg mixture to the flour mixture. Whisk until smooth or free of lumps. Pour in the prepared baking dish and bake for one hour or until toothpick inserted comes out clean. Let cool in the baking pan at least two hours before cutting.
Cut in squares to desired sizes. Garnish with whipped cream and toasted coconut. Drizzle with salted caramel (optional).