Assemble your ingredients.

Grease the sides and bottom of a 13.5 by 9 inch pan. You can do this recipe in a circular pan, but then of course you would have to use a different marbling pattern.

Preheat your oven to 350F.

Dry ingredients

Add PB and milk.

Use a machine for smoother results; ours was broken :)

Should drop off the whisk.

Transfer about half to a 9x13 inches baking pan.

Add the cocoa powder and baking soda to the other half.

I made too much chocolate batter in this recipe; the design should be easier to see. Sorry about that. It should create a more intricate marbling effect.

Drizzle the chocolate portion randomly over the batter.

Use a butter knife to create an S shape from one end to the other.

Rotate 90 degrees and repeat. Continue to do this until you have a fairly intricate marbled pattern. (Once again, sorry for the slipup)

Bake until a knife or toothpick inserted in the center comes out cleanly.

Wait at least 15 minutes or until cooled, and apply white frosting evenly. Then take your chocolate drizzle/sauce/ice cream topping (even a syrupy frosting will do) and repeat the same marbling.

This is what it should look like. Hope you enjoy!