Get your kids to help you turn this simple rolled sponge cake into a proper yule log. Plastic leaves and bugs are optional, but very effective.
1/2 cup all-purpose flour
3/4 tsp baking powder
3/4 cup granulated sugar
1 tsp vanilla
1 cup butter, softened
1/2 cup unsweetened cocoa powder
1/2 tsp vanilla
2 cups icing sugar
1 tbsp milk, (only if necessary)
Preheat the oven to 400°F (200°C). Prepare a jelly roll or cookie pan approximately 11 x 16 in. (28 x 40 cm), with ½ in. (1 cm) sides. Grease it lightly, then line the bottom with parchment paper or waxed paper, and grease the paper lightly.
In a small bowl, mix together the flour and the baking powder. Set aside.
In a mixing bowl, beat the eggs with an electric mixer until foamy. Add the sugar and vanilla, and continue beating until the mixture becomes very light and thick, and has doubled in volume. This will take 5 to 7 minutes. Now gently fold in the flour mixture using a rubber spatula, taking care not to deflate the batter. When the flour is thoroughly mixed in (don't overmix) spread the batter evenly in the prepared pan (carefully smooth out any bumps). Bake for 8 or 9 minutes, until very lightly browned and the cake springs back when you touch it on top. Remove from the oven and let cool for 2 or 3 minutes in the pan.
Now, sprinkle a clean dishtowel with sugar. Loosen the cake from the sides of the pan and (quickly! carefully! watch out!) flip the cake out onto the sugared towel. Peel off the paper (ta da!). With a sharp knife, trim off the crispy edges (and eat them - this is the cook's bonus. While the cake is still warm, gently roll it in the towel (starting with the long side) and let cool completely.
Now make the frosting. In a large bowl, beat the butter with an electric mixer, until creamy. Add all the rest of the ingredients (except the milk), and beat on high speed until smooth and fluffy. Add the milk, one molecule at a time, only if the frosting is too stiff. Remember - you can always add more milk if you need it, but you can't take it away if you've added too much.
Unroll the cake and spread evenly - right to the edges - with about half of the chocolate frosting. Roll up, starting from a long side, as tightly as possible without squishing out the filling. Place on a serving platter. Spread the remaining frosting all over the cake. Decorate in whatever weird and wonderful way you like and refrigerate for at least an hour before serving.