Step 1
Place a rack in lower third of oven; preheat to 425°. Using the tip of a sharp paring knife, pierce skin of 4 medium Italian or globe eggplants (about 1½ lb.) in several places (this will prevent them from trapping steam and exploding when they roast). Transfer to a large rimmed baking sheet; drizzle 2 Tbsp. extra-virgin olive oil over and season generously with kosher salt and freshly ground pepper. Toss to coat evenly.
Step 2
Roast eggplants until skins are darkened in color and insides are tender (a skewer inserted close to the neck should meet with little to no resistance), 45–60 minutes.
Step 3
Meanwhile, heat 1 Tbsp. extra-virgin olive oil in a large skillet over medium-high. Cook 1 medium onion, finely chopped, 2 garlic cloves, thinly slice, and 1 lb. hot Italian sausages, casings removed, stirring occasionally and breaking up sausage into small pieces with a wooden spoon, until onion is softened and translucent and sausage is cooked through, 8–10 minutes.
Step 4
Reduce heat to medium and add ⅓ cup double-concentrated tomato paste, ½ tsp. dried oregano or Italian seasoning, and ¼ cup water; cook, stirring often, until tomato paste darkens slightly, 5–7 minutes. Add ½ cup water and continue to cook, stirring often, until slightly reduced and saucy looking (similar to Bolognese). Taste sauce and season with salt and pepper if needed.
Step 5
Transfer eggplants to a platter or plates, split lengthwise with a paring knife, and open up like a book. Drizzle flesh with oil and season with salt. Spoon sauce over, then top with 4 oz. whole-milk fresh ricotta, dividing evenly. Drizzle with more oil and season with more salt and pepper. Scatter basil leaves on top.