As a kid I used to cut through the yards to go over to my friend Lauren's (Lauren Shay's dad photographed me for Life magazine when I was 6) house. When her grandma Lily was over she'd always make this incredible irresistible chocolate marble cake. I'll never forget how deliciously moist it was. I tried to get the recipe from her mom but she wouldn't share it. Then, I became a professional pastry chef and tried to re-create it, longing for that taste and texture. Unable to get it totally right, I contacted the family again, but they still were holding on tight to it. I've been trying to get this recipe from their mother for 40 years. She finally shared it with me as my wedding gift after badgering her and her husband, Art, her children and her grandchildren. I even talked about it in an interview in the paper to try to apply gentle pressure on them to give it to me. Now this recipe won't die in her recipe file.
Butter and flour a straight-walled 10-inch tube pan. Preheat the oven to 350 degrees F.
In a standing mixer fitted with the paddle attachment, cream the butter until light and fluffy. Add the sugar and continue to mix well. Add the eggs 1 at a time and beat until incorporated.
In a bowl, whisk together the milk and vanilla. In another bowl, whisk together the flour, baking powder, and salt.
Reduce the mixer's speed to low. Alternately add the flour and milk mixture until a smooth batter is formed. Continue mixing for 5 minutes. (It's important to mix for the full 5 minutes.)
Transfer 1/3 of the batter to a bowl and whisk in the cocoa powder. Stir the coconut into the remaining batter.
Pour the coconut batter into the pan; then spoon the chocolate batter around. Run a knife through the batter, cutting the batters together to create a marbled effect. (Do not stir.) Bake until a toothpick inserted into the middle of the cake comes out clean, about 1 hour 15 minutes.
Let the cake cool in the pan. Invert the cake onto a stand or plate, slice, and serve.