Calico Crumb Cake

Ingredients

• 1 teaspoon baking soda 
• 1 cup chocolate chips 
• 1 cup buttermilk at room temperature
• 2 large eggs at room temperature
• 2 cups flour all-purpose sifted (See Notes)
• 0.5 cup brown sugar light packed
• 1 teaspoon salt 
• 1 cup sugar 
• 4 ounces butter unsalted at room temperature (1 stick)
• 2 teaspoons vanilla extract pure
• 0.5 cup walnuts toasted coarsely chopped (See notes)

Equipment

• bowl
• frying pan
• baking paper
• oven
• knife
• wire rack
• blender
• baking pan
• toothpicks
• cake form
• aluminum foil
• microwave

Directions

1. 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.
2. 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.
3. 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.
4. Sift flour, sugar, baking soda, and salt into large bowl.
5. Add butter and beat on medium speed until combined, about 1 minute (mixture will be crumbly).
6. 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.
7. Transfer 1 cup batter to medium bowl. Stir in melted and cooled chocolate.
8. Scrape plain batter into prepared baking pan. Dollop chocolate batter on top of batter.
9. Run a knife through cake batter to create a marble swirl.
10. Sprinkle evenly with sugar-walnut mixture.
11. Bake until a toothpick inserted in center of cake comes out clean, 25 to 30 minutes.
12. 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.
13. Serve.