MAKE THE BROWNIES: Preheat the oven to 350 degrees. Line an 11-by-17-inch baking sheet with parchment paper and spray the parchment paper with cooking spray. Put the chocolate in a medium bowl.

In a medium saucepan, combine the sugar, butter, corn syrup, and water and bring to a boil. Pour the mixture over the chopped chocolate and let stand for about 1 minute, then whisk until smooth. Whisk in the flour and salt, then whisk in the eggs and vanilla until fully incorporated.

Scrape the brownie batter onto the prepared baking sheet and spread it to the edge. Bake for 15 minutes, until the top of the brownie looks dry and crackly. Transfer the baking sheet to a rack to cool, then transfer the baking sheet to the freezer to chill for 30 minutes, until the brownie base is completely firm.

MEANWHILE, MAKE THE COCONUT TOPPING: In a large heatproof bowl, combine the egg whites with the sugar. Set the bowl over a large saucepan of boiling water and whisk the mixture over moderate heat until it is warm to the touch and the sugar is dissolved, about 2 minutes. Remove from the heat.

Using an electric mixer, beat the egg whites at medium-high speed until stiff, glossy peaks form, about 8 minutes. Fold in the shredded coconut, sour cream, vanilla seeds, and grated orange zest, if using. Spread the coconut topping evenly over the brownie base. Bake for 30 minutes, until the coconut topping is lightly golden and set. Transfer to a rack to cool, then cover and refrigerate until firm, at least 4 hours or overnight.

MAKE THE GLAZE: Combine the chopped bittersweet chocolate, butter, and corn syrup in a large bowl. In a medium saucepan, bring the heavy cream to a boil. Pour the hot cream over the chocolate and let stand for 1 minute, then whisk until the chocolate is melted and the glaze is smooth. Let stand until warm to the touch, about 10 minutes.

Meanwhile, using a sharp knife, trim the border of the chilled brownie base to make it neat. Cut the base into 2-inch squares and transfer them to 2 wire racks set over baking sheets. Top each square with an almond. Using a small ladle, pour a thick coating of the chocolate glaze over each brownie bar. Using a small offset spatula, spread the glaze to coat the top and sides completely. (Rewarm the glaze over a pot of simmering water if it gets too thick.) Refrigerate the brownie bars until the glaze sets up, about 1 hour. Serve chilled.

The brownie bars can be refrigerated for up to 3 days.