: In a large bowl or bowl of a stand mixer, whisk together flours and salt.

Make a well in the center and add water, sugar and yeast.

Let stand until yeast is foamy, about 5 minutes.

Add olive oil and mix until just combined.

Knead dough on a lightly floured surface, adding more flour as needed until dough is smooth and elastic, about 10 minutes; OR, knead dough with dough hook in stand mixer, adding more flour as needed until dough pulls away from sides of the bowl and is smooth and elastic, about 5 minutes.

Shape dough into a ball and place in a large bowl.

Top with a bit of olive oil and roll to coat.

Cover bowl with plastic wrap and let rise until doubled, about 1 hour.

Meanwhile, make the filling: Heat a large skillet over medium heat.

Add butter, then add onion.

Cook onion until caramelized, about 15 minutes.

Add spinach and cook until just wilted.

Remove from heat and place in a bowl. Stir in goat cheese.

Place mixture on a cutting board and chop roughly.

Return to bowl and set aside.

Preheat oven to 400 degrees F and lightly grease a 9-by-13-inch casserole dish; set aside.

When dough is doubled, punch down, remove from bowl and roll out on a lightly floured surface into a large rectangle, about 12 by 15 inches.

Divide dough into 15 rectangles.

Top the center of each rectangle with a generous tablespoon or so of filling (be sure to use all the filling).

Lift up the four corners of the dough over the filling and pinch to secure; lift remaining corners and pinch to seal the dough completely around the filling.

Place roll seam-side down in prepared casserole dish.

Repeat with remaining pieces of dough.

Brush rolls with egg wash and sprinkle with red pepper flakes and sea salt to taste.

Bake until rolls are a deep golden brown, about 15-20 minutes.

Remove from oven and sprinkle lightly with grated Parmesan cheese.

Return to oven to melt cheese, about 2-3 minutes.

Remove from oven and serve warm with pizza sauce, if desired.