Soak the corn husks: Bring a large pot of water to a boil. Remove from heat, then add the corn husks. Submerge them under water with kitchen tongs. Set aside for 30 minutes or until they are pliable.
Prep the pineapple: Peel and core the pineapple. Roughly chop three-quarters of the pineapple and place in a large pot. Cut the remaining quarter into small pieces and set aside.
Caramelize the pineapple: Place the pot over low heat and cook, stirring frequently so the pineapple doesn't burn or stick, until all the liquid has been evaporated and the pineapple starts to caramelize, about an hour. Let cool slightly.
Blend: Transfer the cooked pineapple to a food processor or high-powered blender and pulse until it is broken into small pieces. You can also chop fine by hand if you prefer. Set aside.
Cream the butter and sugar: Combine the 1 cup butter and brown sugar in the bowl of a stand mixer fitted with the paddle attachment. Beat on medium until light and fluffy, about 3 minutes.
Add remaining ingredients: Scrape down the sides of the bowl and add the 3 cups masa harina, 1 cup pineapple juice, 1 cup milk, 2 teaspoons cinnamon, 2 teaspoons baking powder, 1 teaspoon vanilla, and 1/2 teaspoon salt. Start mixer on low then increase the speed to medium and beat until the dough is light and airy, about 2 minutes.
Add pineapple: Add the cooked and raw pineapple and continue beating until evenly combined.
Assemble tamales: Remove corn husks from water and set on a baking sheet. Select one large cornhusk that is at least as wide as your hand with the fingers closed. Dry any excess water with a towel and lay on a clean work surface, the wide end towards you. Place about 1/3 cup of the masa in the middle of the lower half of the corn husk and form into a cylinder shape. Roll the corn husk around the masa and fold the pointy end down to seal. Repeat with remaining corn husks and masa.
Steam tamales: Fill the tamales steamer with water up to the line where the steamer rack sits. Line the steamer rack with corn husks that are too small or ripped. Arrange tamales open side-up, leaning them against the side of the steamer and each other so they don't fall over. Cover with the lid and place over medium-high heat. Once the water is boiling and the steamer is filled with steam, lower the heat to medium-low. Steam until masa springs back when you press it with your finger but isn't hard, about 45 minutes to an hour.
Make coconut sauce: Combine the can of cream of coconut, 1/2 cup sugar, teaspoon vanilla, teaspoon cornstarch in a small saucepan and whisk until smooth. Bring to a simmer over medium heat, stirring frequently, until the sauce thickens slightly. Watch closely to prevent it from boiling over. Remove from heat and cover.
Toast coconut: Place 1/2 cup sweetened coconut in a frying pan and place over low heat. Toast, stirring frequently until coconut is fragrant and golden. Be careful, this happens quickly and can easily burn. The minute it turns golden, remove from the pan to a bowl.
Let rest: Once tamales are ready, they will need to finish steaming off the heat. Remove tamales to a platter and cover with aluminum foil to gently finish cooking, about 10 minutes.
Serve: Unwrap tamales and serve drizzled with coconut sauce and toasted coconut on top. I think the tamales are best served warm but can also be eaten room temperature.
