Put eggs, milk and vanilla essence in a large bowl and whisk to combine. Heat 1 tablespoon of the oil and half the butter in a large, non-stick frying pan over a medium heat.
Spread flaked almonds over a small plate. Sprinkle 2 slices of bread with chocolate, and top each with another slice. Dip sandwiches into egg mixture, then press into almonds, to coat.
Heat remaining butter and oil in pan. Add almond-coated, chocolate-filled sandwiches and cook for 1-2 minutes on each side or until golden. Cut into quarters and serve immediately