Whisk water, 2 Tbsp. olive oil and yeast together in a measuring cup until the yeast dissolves. Whisk flour and 2 tsp. salt together in the bowl of a stand mixer fitted with a dough hook. With the mixer on low speed, slowly add water mixture and mix until dough comes together, about 2 minutes. Increase speed to medium and continue mixing until dough is smooth and elastic, about 8 minutes. If dough is very sticky after 4 minutes, add 1 to 2 Tbsp. extra flour.
Transfer dough to lightly oiled bowl, turning to coat with oil, and cover with plastic wrap. Let rise for 30 minutes. Gently press dough to deflate and using a bowl scraper fold the dough partially over itself to the middle, working your way around the dough until it’s all turned in. Cover with plastic and let rise 30 minutes. While dough is rising for the second time, make the sauce and the sausage topping.
For the sauce: Warm olive oil in saucepan, add garlic and cook until fragrant. Add crushed tomatoes, salt, red wine vinegar and red pepper flakes. Bring to a simmer, the reduce heat and keep warm.
For sausage topping: In a medium bowl, combine sausage, garlic, fennel seed, oregano, and basil. Heat a large sauté pan and tear 1/2-inches pieces of the sausage mixture into it. Brown, turning as necessary. Remove from pan to a paper towel-lined plate when not quite completely browned.
Grease 2 Eighth Sheet pans with 1 tbsp. olive oil each. Divide dough in half and add half to each sheet pan, sliding the dough around to coat with oil. Cover each sheet pan with plastic and let rise 30 minutes. With oven rack in middle position, preheat oven to 425°F. Using fingertips, spread the dough to all corners and edges of sheet pans. Drizzle with a little bit of olive oil and sprinkle each crust with 1/2 tsp. salt. Let dough rest 10 minutes.
For Margherita Pizza: Evenly spread one crust with 1/2 cup shredded mozzarella. Spoon 1/2 cup sauce on top of mozzarella. Then add quartered fresh mozzarella slices. Bake until crust is golden brown around the edges and cheese has melted, 17 to 20 minutes. Out of the oven, top with fresh torn basil. Cut into squares and serve.
For Sausage & Red Onion Pizza: Top one crust with 1/2 of the chopped mozzarella. Distribute the cooked sausage evenly over the crust and add the remaining chopped mozzarella. Top with red onion slices. Bake until crust is golden brown around the edges and cheese has melted, 17 to 20 minutes. Cut into squares and serve. Makes 2 Eighth Sheet Pan pizzas.
