Take everything out of the refrigerator so that all ingredients
can come room temperature.
Preheat the oven to 350 degrees F.
Put all the cake ingredients: flour, sugar, baking powder and soda,
cocoa, butter, eggs, vanilla, and sour cream into a food processor and
process until you have a smooth, thick batter. If you want to go the
long way around, just mix the flour, sugar and leavening agents in a
large bowl and beat in the soft butter until you have a combined and
creamy mixture. Now whisk together the cocoa, sour cream, vanilla, and
eggs and beat this into your bowl of mixture.
Divide this batter, using a rubber spatula to help you scrape and
spread, into the prepared tins and bake until a cake tester comes out
clean, which should be about 35 minutes, but it is wise to start
checking at 25 minutes. Also, it might make sense to switch the 2 cakes
around in the oven halfway through cooking time. Remove the cakes, in
their tins, to a wire rack and let cool for 10 minutes before turning
out of their tins. Don't worry about any cracks as they will easily be
covered by the frosting later.
To make this icing, melt the chocolate and butter in a good-sized
bowl either in the microwave or suspended over a pan of simmering water.
Go slowly either way: you don't want any burning or seizing.
While the chocolate and butter is cooling a little, sieve the
confectioners' sugar into another bowl. Or, easier still, put the icing
sugar into the food processor and blitz to remove lumps.
Add the corn syrup to the cooled chocolate mixture, followed by the
sour cream and vanilla and then when all this is combined whisk in the
sieved confectioners' sugar. Or just pour this mixture down the funnel
of the food processor onto the powdered sugar, with the motor running.
You may need to add a little boiling water, say a teaspoon or so,
or indeed some more confectioners' sugar, depending on whether you need
the frosting to be thiner or thicker. It should be liquid enough to coat
easily, but thick enough not to drip off.
Choose your cake stand or plate and cut 4 strips of baking
parchment to form a square and sit 1 of the cakes, uppermost (i.e.
slightly domed) side down.
Spoon about 1/3 of the frosting onto the center of the cake-half
and spread with a knife or spatula until you cover the top of it evenly.
Sit the other cake on top, normal way up, pressing gently to sandwich
the 2 together.
Spoon another 1/3 of the frosting onto the top of the cake and
spread it in a swirly, textured way (though you can go for a smooth
finish if you prefer, and have the patience). Spread the sides of the
cake with icing and leave a few minutes until set, then carefully pull
away the paper strips.
I love to dot the top of this with sugar pansies, and you must
admit, they do look enchanting, but there really is no need to make a
shopping expedition out of it. Anything, or indeed nothing, will do.