Attempt two: same recipe for the cake, but I lowered the temperature to 350. Also, I followed the technique in World Class Cakes of painting when it first comes out of the oven, filling, and then rolling inside the towel. I had issues with cake sticking to the towel (should have sprinkled flour on the towel as in the first method), and the filling melted as I rolled. I did put it into the refrigerator still rolled in the towel, and was thus able to save something. I covered the roll in whipped cream and decorated with the meringue mushrooms.
Lessons for take 3:
1. Roll long side. I was rolling from the short side which I think is what contributed to the cracking in take 1. Neither recipe mentioned rolling from the long side.
2. Follow Washington Post method of assembling - sprinkle powdered sugar on towel, flip out cake, peel off parchment paper, dust cake with sugar, place clean side of parchment paper back on cake, and pre-roll long side. Make the roll as tight as possible, and let cool to room temperature.
3. Melt the chocolate into the whipping cream before starting the cake so it has plenty of time to cool if you use the same filling. I think the chocolate Mascarpone mouse was a little too much with the chocolate cake.
4. Bake at 375, but check at 7 minutes. I think my second cake was slightly underdone which contributed to it sticking to the towel.
5. The meringue mushrooms came out perfectly. Definitely do those again.