Pre heat the oven to 450f (230c) with a rack in the centre of the oven. Place 2 tablespoons of butter in a 10 inch skillet, pie dish or other oven safe dish. Put the skillet in the oven to melt the butter, taking care to not burn the butter.
In a small sauce pan, melt the remaining 2 tablespoons of butter and set aside to cool slightly.
In a blender, combine the eggs, buttermilk, flour, vanilla and salt. Blend on low for a minute. Stop the blender and scare down the sides. With the blender on low, slowly start to add the butter to the batter in a steady stream. Mix for a further 30 seconds until the butter is incorporated and the batter is smooth.
Remove the hot skillet from the oven and carefully pour the batter into the pan. Don’t mix the batter any further. Return the pan to the oven and bake for about 20-25 minutes. Don’t open the oven for the first 15 minutes of baking, or your Dutch baby may collapse.
Once the Dutch baby pancake is golden and risen, remove from the oven and dust with icing sugar and serve with cream, maple syrup and fruit.