This recipe is adapted from Better Homes & Gardens Pies and Cakes, 1972 edition.
Notes: Sift the flour, then measure out the amount called for in the recipe. To toast the walnuts: arrange walnuts in single layer on baking sheet. Bake in center rack in preheated 350°F oven until fragrant and golden, 7 to 10 minutes, shaking pan halfway through baking to redistribute pecans. Transfer baking sheet to cooling rack and cool pecans completely before chopping.
- Active time: 30 minutes
- Total time:2 hours
- For the Topping:
- 1/2 cup all-purpose flour
- 1/2 cup packed light brown sugar
- 2 tablespoons unsalted butter, chilled and cut into small pieces
- 1/2 cup toasted walnuts, coarsely chopped (See notes)
- For the Cake:
- Baking spray
- 1 cup bittersweet chocolate chips
- 2 cups sifted all-purpose flour (See Notes)
- 1 cup sugar
- 1 teaspoon baking soda
- 1 teaspoon salt
- 4 ounces (1 stick) unsalted butter, at room temperature
- 2 large eggs, at room temperature
- 1 cup buttermilk, at room temperature
- 2 teaspoons pure vanilla extract
Adjust oven rack to middle position and preheat oven to 350°F. Lightly spray 13- by 9-inch cake pan with baking spray. Line pan with parchment paper or heavy-duty foil lengthwise with one sheet, then crosswise with a second sheet to create a sling; spray once again with baking spray.
For the topping: Combine flour and brown sugar in medium bowl. Using two dinner knives, cut in butter until mixture is resembles wet sand. Stir in nuts; set aside.
For the cake: Place chocolate in small bowl and microwave until smooth and melted, 1 to 2 minutes, stopping microwave to stir chocolate every 30 seconds. Set aside and allow to cool.
Sift flour, sugar, baking soda, and salt into large bowl. Add butter and beat on medium speed until combined, about 1 minute (mixture will be crumbly).
In small bowl, beat together eggs, buttermilk, and vanilla. With mixer on medium-low speed, add egg mixture in slow steady stream. Beat just until combined. Pause mixer, scrape sides and bottom of bowl, then beat mixture on medium-high speed until thoroughly combined, about 30 seconds.
Transfer 1 cup batter to medium bowl. Stir in melted and cooled chocolate.
Scrape plain batter into prepared baking pan. Dollop chocolate batter on top of batter.
Run a knife through cake batter to create a marble swirl. Sprinkle evenly with sugar-walnut mixture.
Bake until a toothpick inserted in center of cake comes out clean, 25 to 30 minutes. Transfer cake to cooling rack and cool in pan 10 minutes. Pull cake out onto a cooling rack using the parchment sling and cool completely, about 1 hour. Serve.