Vanilla and Cocoa Marble Cookies

👨‍🍳 Method

To assemble

1. 1
   Preheat the oven to 175°C (345°F) and line a baking sheet with parchment paper.

   ⚙ Preheating the OvenOven

   💡Put things in the oven only once it's reached temperature, after the heating light has gone off: an oven that hasn't reached temperature changes baking times, and the bake burns outside or stays underbaked.
2. 2
   Whip the soft butter with the powdered sugar, to a smooth, pale mixture.

   ⚙ WhippingBowlHand mixerorStand mixerorWhisk

   💡Cream the butter soft, at room temperature: cold butter doesn't take in air, and melted butter doesn't hold it.
3. 3
   Add the yolks and vanilla and mix well.
4. 4
   Add the flour and salt and mix just until a dough forms.

   💡Mix in the flour only until a dough forms: long kneading develops gluten, and the cookies come out hard instead of crumbly.
5. 5
   Divide the dough in two and knead the cocoa and the milk into one half.

   Bowl
6. 6
   Roll out both doughs, each one between two sheets of parchment paper into a 20 by 30 cm rectangle.

   ⚙ Rolling Out DoughRolling pinParchment paper

   💡Roll from the center outward and give the dough a quarter turn between rolls: this keeps it even in thickness and stops it sticking to the counter. If it springs back, cover for 10–15 minutes and try again.
7. 7
   Lay the light dough on the dark one and roll up tightly from the long side.
8. 8
   Wrap the roll in plastic wrap until it holds together and chill 45 minutes.

   ⚙ Wrapping and Chilling the DoughPlastic wrapRefrigerator
9. 9
   Slice the roll with a sharp knife into 7 mm-thick cookies and arrange on the baking sheet, spaced apart.

   KnifeCutting boardBaking pan
10. 10
    Bake 12–14 minutes, until the edges of the light part start to turn golden.

    ⚙ BakingOvenBaking pan

    💡Take the cookies out while they still look soft: they firm up as they cool, and long baking dries them out.

    💡Check by the cue (until…), not just the clock: every oven bakes a little differently.
11. 11
    Cool 10 minutes on the pan: the cookies firm up as they cool.