All ingredients ready? Let's begin!
In a large mixing bowl, add the warm water, yeast, and sugar. Stir gently. Allow this to sit until the yeast starts to foam or bubble, approximately 7 minutes.
Gently stir in the salt and 2 tablespoons of the olive oil. Add the flour and stir with a wooden spoon until a sticky ball of dough forms.
Lightly flour a clean work surface. Turn the ball of dough onto the floured surface and knead with your hands for at least 5 minutes and up to 15 minutes. Here is a video that shows how to knead dough by hand.
Wipe out the mixing bowl. Coat it lightly with olive oil.
Place the ball of dough in the bowl and cover with a clean kitchen towel or plastic wrap. Place the bowl in a turned-off oven or microwave and allow it to sit for 1-1/2 to 2 hours until doubled in size.
While the dough is rising, prepare the filling: In a large skillet over medium-high heat, add the remaining 2 tablespoons of olive oil and the sliced onions. Sauté for 5 minutes until the onions become fragrant.
Add the garlic, Italian seasoning (if using), and the sausage. Break the sausage up with a wooden spoon. Cook until the sausage is browned and no longer pink, stirring occasionally. Remove the pan from the heat and season with salt and pepper to taste. Allow the filling to cool.
Line a sheet pan with parchment paper or grease it with olive oil.
Lightly flour a large work surface. Place the risen dough on the floured surface and flatten it out with your hands. Dust the top of the dough with flour and roll it out with a rolling pin into a rectangle that is about 16 x 24 inches.
Spoon the filling over the dough and spread it out evenly. Start rolling the 24-inch side of the dough over the filling until you have a long log shape. Form the roll into a donut shape with the two ends meeting. Pinch the ends to seal the roll.
Transfer the circle of dough to the sheet pan. Using a sharp paring knife, cut a few slits in the top of the roll to allow some steam to escape. Place a clean kitchen towel over the roll and allow it to rest for 45 to 60 minutes to rise again.
Preheat the oven to 400°F.
Brush the roll with olive oil. Place the pan in the oven and bake for 15 minutes. Reduce the heat to 350°F and continue to bake for another 20 to 25 minutes until the dough is golden brown. Remove the pan and allow the bignolati to cool for 10 minutes.
Using a serrated bread knife, slice the bignolati into 1-1/2-inch thick pieces and serve with napkins. Enjoy with your hands. You can serve this with a warm marinara dipping sauce.