Heat the oven to 180 degrees. Lubricate the cake pan with butter.
In a saucepan, boil beer with oil over medium heat. Add cocoa and mix to make the mixture homogeneous. Cool a little.
Mix flour, sugar, soda and salt. Beat the egg with sour cream with a mixer. Pour beer and chocolate into the egg-sour cream mixture and mix. At medium speed, continue to whisk and gradually pour the dry mixture. Knead the dough.
Pour the dough into the prepared pan.
Bake for 40-45 minutes. Check with a toothpick for preparedness. Put the pie on a dish. Serve with melted hot chocolate.