Preheat the oven to 350° and grease an 8x8 pan.

In a large, microwave-safe bowl, combine the butter and chocolate chips, and microwave at 30-second intervals, stirring after every 30 seconds, until the chocolate chips have melted. Let cool slightly, then stir in the sugar.

Stir in the eggs, one at a time, beating well after each egg. Stir in the vanilla extract.

In a small bowl, whisk together the cornstarch, cocoa powder and salt. Add the cornstarch mixture to the brownie batter, and stir for 1-2 minutes, until well-combined.

Pour the brownie batter into the greased pan, and bake at 350° for 35-40 minutes, until a tester comes out with a few crumbs attached.

Let the brownies cool completely before serving.

Combine the butter, egg yolk, sugar and evaporated milk in a small saucepan. Cook over low heat, stirring occasionally, until the sauce thickens (about 6 minutes).

Remove the saucepan from the heat, and immediately stir in the chopped pecans and shredded coconut. Serve immediately, or transfer to a glass jar and refrigerate until ready to assemble the sundaes. (If serving later, warm the topping in the microwave for 1-2 minutes.)

To assemble the sundaes, top each brownie with a scoop of ice cream, then top with a few spoonfuls of the warm German chocolate topping, and enjoy!