Ingredient Note: Whole-wheat pastry flour is milled from soft wheat. It contains less gluten than regular whole-wheat flour and helps ensure a tender result in delicate baked goods while providing the nutritional benefits of whole grains. Available in large supermarkets and in natural-foods stores. Store in the freezer.
To prepare cake: Preheat oven to 350°F. Coat a 9-by-13-inch baking dish with cooking spray.
Toast walnuts in a small baking pan in the oven until fragrant, 5 to 10 minutes.
Whisk flour, baking soda, salt and cinnamon in a medium bowl. Whisk eggs, sugar, buttermilk, oil, vanilla and 1/4 cup of the reserved pineapple juice in a large bowl until blended. Stir in pineapple, carrots and coconut. Add the dry ingredients and mix with a rubber spatula just until blended. Stir in the nuts. Scrape the batter into the prepared pan, spreading evenly. e the cake until the top springs back when touched lightly and a toothpick inserted in the center comes out clean, 40 to 45 minutes. Let cool completely on a wire rack.
To prepare frosting & finish cake: Place coconut in a small baking pan and toast in the oven at 300 degrees F, stirring several times, until light golden, 5 to 10 minutes. eat cream cheese, confectioners sugar and vanilla in a mixing bowl with an electric mixer until smooth and creamy. Spread the frosting over the cooled cake. Sprinkle with the coconut.