Preheat the oven to 425°F. Place a 10” cast iron skillet on a middle rack to warm along with the oven.
In a food processor or blender, puree the eggs. Blend over high speed until light and frothy, about 30 seconds to 1 minute.
Add buttermilk, blend another 30 seconds
Add flour, vanilla, cardamom, soda and salt. Blend another 30 seconds to 1 minute or until smooth.
OPTIONAL: Rest the batter: leave in blender and set aside to rest 20 to 25 minutes. This gives the flour time to absorb the liquid.
After the 20 minute batter rest (optional), carefully remove the hot cast iron skillet from the oven.
Place the cubed butter in the pan, it will immediately bubble and begin to melt.
Place the skillet with the butter back into the oven until the butter just begins to toast (it will smell nutty and fragrant) for 45 seconds to 1 minute, watch carefully to not burn.
Remove the skillet from the oven, swirl to coat the pan evenly.
Pour the Dutch baby batter into the center of the skillet and immediately place back into the oven. Bake for 12 to 20 minutes (depends on pan size), or until the Dutch baby has risen substantially and is golden brown.
Serve immediately: You can either serve from the pan or transfer the Dutch baby to a serving platter. Dust with powdered sugar, fill center with whipped cream, top with brandy roasted rhubarb and berries of choice.