Soft cocoa flavored yeasted dough surrounds a chocolate filling. A cinnamon roll but double the chocolate!

A twist on my double chocolate babka: a chocolate dough and filling, but shaped like a traditional cinnamon roll. While cream cheese would be a wonderful topping here, I went for something a bit more fancy: caramelized white chocolate ganache. The sweetness of the ganache pairs perfectly with the dark chocolates used in the bread.
In the bowl of a stand mixer, add the yeast, sugar and water. Let stand until frothy.
Add the eggs, yolk, honey, oil and vanilla and whisk to combine.
Add the cocoa, salt and flour. Let the mixer knead the dough for 5-10 minutes, until it is a sticky mass.
Put the dough into a well-oiled large bowl, turning to coat in the oil. Cover with plastic wrap and either set it in the fridge for an overnight rise, or in a warm place for a 2 hour rise.
Make the filling: melt the butter and chocolate together in a warm saucepan (keep the heat low) and then sift in the powdered sugar and cocoa. Stir in the vanilla.
Prepare a 13 x 9 inch cake pan with parchment paper.
Roll out the dough on a well-floured surface into a large rectangle, about the size of a cookie sheet.
Spread the filling over the dough, leaving a half inch border at the top. Roll the dough bottom up (from the longer side) into a coil.
Using a sharp knife or wax-free floss, slice the coil into 1 inch pieces.
Arrange the slices on the pan like in the photo.
Set the dough in a warm place to rise again. If you had the first rise in the fridge, the dough will need about 1 1/2 hours or 2 to rise fully. If you did a room temperature rise, it will only need 45 minutes.
Preheat oven to 350. Bake the rolls for about 25 minutes. Check for doneness by pressing the dough lightly with your finger to see if it feels heavy and doughy.
Let the rolls cool and make the ganache by warming the cream, then pouring it over the chopped caramelized white chocolate. Stir until the ganache is smooth.
When rolls are completely cool, pour the ganache over them. Top with flakes of sea salt, if desired.
how big of a cookie sheet when you say to roll it out that big?
A standard cookie sheet (baker’s half), so 18 x 13".