Place the flour, salt, baking powder, bicarbonate of soda, sugar and vanilla seeds in a food processor and pulse briefly to blend. Add the egg yolks, butter, buttermilk and milk, then whizz to a smooth batter, scraping down the sides of the bowl once or twice. Whisk the egg whites in another bowl to soft, floppy peaks, then fold into the batter.
Heat a heavy-bottomed frying pan until you can feel a good heat rising, then lightly oil the pan. Using a small ladle, pour in the batter to make pancakes about 10cm in diameter. Cook for about 1 min until the tops are set and little holes appear in the surface. Flip the pancakes over, brown lightly on the other side, then transfer to a tea towel placed on a wire rack and keep warm in a low oven. Repeat with the remaining batter, stacking the pancakes as they are cooked.
To serve, pour the sugar into a mixing bowl and toss the Brazil nuts and bananas through it. Tip into a pan, heat through to melt the sugar, then toss together as everything begins to caramelise. When the nuts and bananas are golden brown, remove from the heat and stir in the maple syrup. Arrange the pancakes on a serving dish and spoon over the nut and banana mix, then serve with extra syrup and a dollop of yogurt or creme fraÃ®che.