Bring the vegetable broth to a simmer in a medium saucepan. Keep the broth warm over very low heat.
Meanwhile, add the olive oil, 2 tablespoons of butter, diced onion, and garlic to a heavy large saucepan. Cook, stirring occasionally, for about 5 minutes over medium heat.
Stir in the rice and let it toast for a few minutes. Add the wine and cook, stirring continuously, until fully absorbed.
Add 1 cup of the hot vegetable broth to the rice, and stir until the broth is absorbed. Continue adding broth, 1 cup at a time, stirring continuously, until the rice is just tender and the risotto is smooth and creamy (about 25-30 minutes).
Reduce the heat to low, stir in the fresh spinach, and cook until fully whilted (5 minutes).
Stir in the remaining butter and Parmesan cheese.