Place the cauliflower florets in a large pot, cover with water, and bring to a boil. Reduce heat to low, cover, and simmer until very soft, about 22 minutes.
Drain the cauliflower in a colander and let cool slightly until it is safe to handle.
In batches, transfer cauliflower to a clean dish towel or cheesecloth, gather the cloth, and squeeze out as much liquid as possible. Place the drained cauliflower in a large bowl and repeat with remaining cauliflower.
Add the flour and kosher salt to the drained cauliflower. Mix with a fork, then use your hands to fold and squeeze until a cohesive dough forms. If the dough is very sticky, you may dust your hands with a little extra flour.
Lightly dust a work surface with flour and divide the dough into 8 equal pieces. Roll each piece into a rope about 10 inches long and 1/2 inch thick.
Cut each rope into 13 equal pieces to make gnocchi; gently separate them so they do not touch. You should have about 108 pieces total.
Heat a large skillet over medium and lightly mist with olive oil spray. Working in two batches to avoid overcrowding, add half the gnocchi to the skillet.
Let the gnocchi cook undisturbed for 2 minutes, then gently flip with a spoon or tongs and sprinkle with a little salt. Cook another 2 to 4 minutes until lightly browned and cooked through. Remove to a plate and repeat with the remaining gnocchi.
Return all gnocchi to the skillet, pour the marinara sauce over them, stir gently to coat, and warm through. Serve with grated Parmesan and basil if desired.