Using a large mortar and pestle, combine extra-virgin olive oil, minced garlic, dried rosemary, and dried minced onion. Crush together until rosemary is in small pieces. Allow to set for 10 minutes to infuse flavors.
Prepare the Sourdough
In a large mixing bowl, combine the active sourdough starter, warm water, dried milk powder, instant yeast, granulated sugar, kosher salt, and all-purpose flour. Add in 3 tablespoons of the rosemary-garlic oil.
Using a dough hook, mix together until combined and knead for 5-7 minutes. Place in a greased bowl and cover. Allow to rise for 1 hour.
Preheat oven to 450 degrees at least 30 minutes prior to baking along with a pizza stone. Use convection oven if that is an option for you.Lay out 2 pieces of parchment paper 10" x 15" and spray with baking oil.
Divide the dough into four pieces and form each into a ball. Place 2 dough balls on each of the parchment papers. Spread each out to form 11" x 5" ovals.
Lightly brush each with remaining rosemary-garlic oil. Allow to rise for 40-50 minutes.
When ready to bake, sprinkle each with sea salt and freshly ground black pepper, as desired.
Bake two at a time on a hot pizza stone for 4-7 minutes until a deep golden brown. Repeat with remaining dough. Serve warm. Makes 4 pieces of flat bread.
Notes
*Use convection setting on your oven if you have that option.