Preheat oven to 350°F. Spray a 9-inch pie plate with nonstick spray.

In a medium saucepan combine 1/2 cup granulated white sugar, 2 tablespoons butter, and 2 tablespoons water. Cook over medium heat, stirring occasionally, until the mixture comes to a boil. Remove from heat.

Immediately add 1 1/3 cups semi-sweet chocolate chips to the hot mixture and stir until melted and smooth. Let the chocolate mixture cool 2–3 minutes (warm but not piping hot).

Add 2 large eggs to the chocolate mixture and beat with a spoon until well blended.

In a separate bowl stir together 2/3 cup all-purpose flour, 1/4 teaspoon baking soda, and 1/4 teaspoon salt. Add the dry ingredients to the chocolate-egg mixture and stir until just combined. Stir in 1 teaspoon vanilla extract.

Pour the batter into the prepared pie plate and smooth the top. Bake 25–30 minutes, until the edges are set and the center is almost set (the center will remain slightly soft). For a gooier center, remove closer to 25 minutes.

While the pie bakes or after removing it from the oven, make the fudge sauce: in a medium microwave-safe bowl combine 1 cup semi-sweet chocolate chips, 1/2 cup evaporated milk, 1/4 cup granulated white sugar, and 1 tablespoon butter. Microwave on HIGH 1 minute; stir. If necessary, microwave an additional 15 seconds at a time, stirring after each, until the mixture is smooth and the chips are fully melted.

Let the pie rest about 5 minutes to allow the center to set slightly. Slice and top each warm slice with 1/3-cup scoops of vanilla ice cream (use the 3 1/3 cups as needed) and drizzle with the warm fudge sauce. Serve immediately.