Melt butter and chocolate over a double boiler or in a microwave (use a microwave safe bowl. Melt for 25 seconds. Whisk. Repeat process until everything has melted and you have a smooth chocolate-butter mixture).
Add sugar and whisk well.
Add the vodka, mix and check if the mixture has cooled down.
Add the two eggs to the cooled down mixture (if the mixture is warm, the eggs could get partially cooked).
Whisk the eggs into the mixture. Add the flour in two batches and again, mix well to make a uniform batter.
Transfer the batter to a greased pan and bake at 350°F (180°C). Bake for about 25 min or until a fork inserted comes out ALMOST clean. We want the centre to be a tad moist and gooey unlike a cake.