Preheat oven to 350F and grease two 9-inch round cake pans, lining bottoms with parchment paper. Whisk together gluten free flour, sugar, cocoa powder, baking soda, and salt in a large bowl.
Add eggs, buttermilk, vegetable oil, and vanilla extract and beat on medium speed for 2 minutes. Stir in hot water until the batter is smooth and well combined. Divide evenly between the prepared pans.
Bake for 30 to 35 minutes until a toothpick comes out clean. Cool in pans for 10 minutes, then turn out onto wire racks to cool completely.
For the frosting, combine evaporated milk, sugar, egg yolks, and butter in a medium saucepan over medium heat. Cook, stirring constantly, for 10 to 12 minutes until the mixture thickens and turns golden.
Remove from heat and stir in vanilla extract, shredded coconut, and chopped pecans. Let cool until thick enough to spread, about 30 minutes.
Place one cake layer on a plate, spread half the coconut pecan frosting over the top, place the second layer on top, and spread the remaining frosting over it. Serve at room temperature.