Line the bottom of a 17 ¼ x 11 ½ x 1” (43.8 x 29.2 x 2.54 cm) jellyroll pan with parchment paper.
Sponge:
With a mixer, beat eggs, sugar and vanilla together until thick and light yellow. In a separate bowl, combine crushed cereal flour, cinnamon and baking soda; add to egg mixture all at once and blend on low speed while slowly adding the hot water.
Pour batter into the prepared pan and spread evenly. Bake for 15 minutes or until sponge is lightly golden.
Remove from oven and run a knife around the edges. Cool at room temperature for up to four hours.
Filling;
in a bowl, whip cream until starting to thicken, add icing sugar and cocoa powder and whip until soft peaks form.
Add sour cream and whip until peaks form. Gently fold in chopped chocolates.
Invert sponge onto a fresh piece of parchment paper; peel off parchment backing.
Spread the filling leaving a 1/2 –inch (1 cm) border at the finished edge. Using the parchment as a support, roll sponge from the short side.
Place on a platter seam side down.
Cover and refrigerate for one hour or more. Dust log with icing sugar, or cover with your favorite butter cream icing. Decorate as desired.