Tunnel of Fudge Cake

This cake rose to popularity after the recipe was entered into the Pillsbury Bake-off sometime in the 1960s.  Pillsbury discontinued the packaged frosting mix that was used in the original recipe, so bakers everywhere (or maybe not everywhere - I have nothing to back this claim up) set out to re-create this classic.  The first time I attempted to make this cake I was using a terrible quality bundt pan, the cake didn't come out of the pan, disaster ensued, and I ended up with tunnel of fudge cake balls.  Now I have a nice, high quality Nordicware anniversary bundt pan, and all is right with the world.  The cake turned out to be deliciously dense and rich.  The fudge center tasted almost like brownie batter.  Do not omit the nuts from this recipe, as they are important to achieving the proper consistency.

 This picture isn't great, but it does a nice job of showing off the fudgy center.

TUNNEL OF FUDGE CAKE
Adapted from The America's Test Kitchen Family Baking Book

INGREDIENTS - CAKE
1/2 cup boiling water
2 ounces bittersweet chocolate, chopped
2 cups all-purpose flour
2 cups walnuts, chopped fine
2 cups confectioners' sugar
3/4 cup Hershey's Special Dark cocoa powder or Dutch-processed cocoa powder
1 teaspoon salt
2 1/2 sticks unsalted butter, softened
1 cup granulated sugar
3/4 cup packed light brown sugar
1 tablespoon vanilla extract
5 large eggs, room temperature

INGREDIENTS - GLAZE
4 ounces bittersweet chocolate, melted
1/3 cup heavy cream, hot
2 tablespoons light corn syrup
1/4 teaspoon vanilla extract
pinch salt

DIRECTIONS
1. Adjust oven rack to the lower-middle position and heat the oven to 350 degrees.  Grease and flour a 12-cup bundt pan or spray pan liberally with bake release spray.

2. Whisk the boiling water and chopped chocolate together in a small bowl until melted and smooth.  Let the mixture cool slightly.  In a medium bowl, whisk the flour, nuts, confectioners' sugar, cocoa, and salt together.

3. In a large bowl, beat the butter, granulated sugar, brown sugar, and vanilla together with an electric mixer on medium speed until light and fluffy - about 3-6 minutes. Beat in the eggs, one at a time, until combined, about 1 minute. Beat i the chocolate mixture until combined, about 30 seconds. Reduce mixer speed to low and slowly beat in the flour mixture until just incorporated, about 30 seconds.

4. Scrape the batter into the prepared pan and smooth the top. Wipe any drops of batter off the sides and gently tap the pan on the counter to settle the batter. Bake the cake until the edges begin to pull away from the sides of the pan and the top feels springy when pressed with a finger, about 45 minutes.  Do not overbake.

5. Let the cake cool in the pan for 10 minutes, then flip it out onto a wire rack to cool. Let the cake cool completely, about 2 hours.

6. For the glaze, whisk all of the glaze ingredients together in a medium bowl until smooth. Let sit until thickened, about 25 minutes.

7. After the cake has cooled completely, drizzle the glaze over the top and sides of the cake.  Let the glaze set, about 25 minutes, before serving.