Preheat the oven to 375 degrees.
On the stovetop, heat a 12- inch cast-iron skillet over medium-high heat, add the butter and olive oil, and allow them to melt.
In a bowl, whisk together the sourdough starter, baking soda and powder and salt.
Pour the batter into the skillet and sprinkle with the rosemary or herb mix.
Allow the dough to cook on the stovetop for 3-4 minutes to develop a lightly brown crust.
Transfer skillet to the oven. Bake for 10-12 minutes, until golden in color.
Drizzle with a little bit of olive oil and garnish with fresh rosemary. Cut into wedges and enjoy!