For the pancake: preheat the oven to 425 degrees F. Put the butter in a glass 9X13-inch baking dish and pop the pan in the oven while it preheats (if it's taking a while to mix up the batter, keep an eye on the dish so the butter doesn't burn; take it out when the butter is melted). Swirl the melted butter to coat the bottom of the 9X13-inch pan and set aside.
Combine all the pancake ingredients in a blender and process until smooth and well-combined, 20-30 seconds.
Pour the batter into the prepared pan and immediately return to the oven. Bake for 20 minutes until the pancake is puffy and lightly browned on the bottom and edges.
Serve immediately with jam, butter syrup, maple syrup or whatever else your heart desires.
For the syrup: in a larger than you think saucepan (it will foam and triple in volume at the end), combine the sugar, buttermilk and butter and bring to a boil, stirring often. Reduce the heat and simmer for 5-7 minutes. Off the heat, stir in the vanilla and baking soda until well-combined. Serve warm over pancakes. For an extra caramelly version, add the baking soda at the beginning with the buttermilk.
Notes
Oven Temp: the original recipe had a temperature of 400 degrees F. If that's worked for you, continue to use it! The last couple of years I've set the oven to 425 degrees F - the pancake puffs better and the edges are especially golden and yummy.