Coarsely chop spinach. Stem and coarsely chop parsley. Mince garlic. Slice pepperoncini into 1/4” rounds. On a separate cutting board, remove Italian sausage from casing.

Heat a medium non-stick pan over medium heat. Add Italian sausage to hot pan and cook until meat is browned and no pink remains, 6-7 minutes. Set aside. Measure out 1/4 cup self-rising flour and set aside. This "bench flour" is used to prevent dough from sticking. Reserve for dusting work surface, hands, and rolling pin. Stir together remaining flour, Greek yogurt, 1 Tbsp. olive oil, and 1/2 tsp. salt in a large mixing bowl.

Dust a clean work surface with reserved bench flour. Turn dough out of bowl onto dusted surface and knead, folding dough over on itself and pressing down with heel of your hand, 5 minutes. Don't worry if dough is shaggy at first; keep kneading and it will turn into a smooth elastic ball. Once dough is smooth, divide into two equal balls. Using a rolling pin or bottle, roll dough into two 6"x10” rectangles, dusting surface and dough with bench flour.

Transfer rolled dough rectangles to baking sheet. We recommend rolling dough onto your rolling pin and unrolling onto baking sheet or gently folding dough, transferring, and unfolding. Leaving 2" exposed on ends, add 2 Tbsp. sauce to each rectangle. Divide sausage, spinach, mozzarella, and pepperoncini (to taste) between each dough rectangle. Top each with another 2 Tbsp. sauce (reserve remaining for dipping).

Cut slits on long edges of dough 1” apart and 1 1/2" deep to form strips. Fold top edge over filling. Then, starting at the top, fold each strip towards center to cover filling, alternating left and right (like a braid). Tuck ends up and under before last "braid." Bake 15 minutes. Place a small pan over medium heat. Add butter and garlic and melt butter completely, 1-2 minutes. Remove stromboli from oven, brush with garlic butter, and bake until browned, 8-10 minutes. Rest at least 5 minutes before serving.

If desired, slice stromboli into 1” slices, or dig in with a knife and fork. Place any remaining sauce in a small dish for dipping. (We prefer it warmed, either in a small pan or 15 seconds in a microwave.) Garnish stromboli with parsley.