Preheat the oven to 325 degrees F. Toast the almonds on a baking sheet in the oven stirring occasionally, until golden, 7 to 10 minutes. Cool; set 1/2 cup of the almonds aside. In a food processor; pulverize the remaining almonds with the sugar. Add the bread and pulse the machine until reduced to fine crumbs. Drizzle in the melted butter and pulse to mix thoroughly. Evenly pat the mixture over the bottom and sides of a 3/4-inch deep, 9-inch tart pan with a removable bottom. Refrigerate several minutes to set.
Twist a corkscrew (or dive an ice pick or screwdriver) into 2 of the coconut's "eyes" (the dark indentations on one end), then drain the trapped liquid into a cup (strain if it contains any bits of coconut shell). Place the coconut on a baking sheet and put into the oven for about 15 minutes to help loosen the flesh from the shell. With a hammer crack the coconut into several pieces, then use a small knife or screwdriver to pry the flesh from the shell. Use a paring knife or a vegetable peeler to peel away the dark brown skin.
In a food processor (or, with determination and stamina, using a four-sided grater) grate the coconut into medium fine shreds. Measure out 2 1/2 cups for the pie; reserve the remainder for the garnish. Raise the oven temperature to 350 degrees F. In a small (1 to 1 1/2 quart) saucepan, combine the coconut water, cream and sugar. Simmer over medium heat, stirring frequently, until reduced to 1 cup, 10 to 15 minutes. Pour into a large bowl, then stir in the 2 1/2 cups of coconut, the reserved 1/2 cup almonds, the egg yolks and vanilla. Set the prepared crust onto a baking sheet, scoop in the coconut filling and bake in the middle of the oven until set and lightly browned on top, 30 to 35 minutes. Cool on a wire rack.
While the pie is baking, toast the reserved coconut on a baking sheet in the oven, stirring occasionally, until nicely browned, 7 to 10 minutes. Cool the pie completely and slice. Place the pie back in the oven and heat for 10 minutes. Serve with sour cream and coconut.
Recipe from Rick Bayless's Mexican Kitchen; Published by Scribner, 1996