Slice the squash lengthwise and remove the seeds. Spray lightly with olive oil and place in the preheated oven, cut side up. Roast the squash for about 1 hour, until slightly tender.

Remove from the oven and let cool. The squash will have a small amount of liquid in the cavity. After it is cool, drain the liquid and place the squash on a cutting board, cut side down.

Gently peel the skin away from the squash. Slice across the squash parallel to the cutting board, dividing into three slices. Keep the shape of the squash intact. Slice lengthwise at about 1/4 inch intervals and then crosswise, so as to divide into 1/2 inch cubes. Set aside.

Slice the root off of the leek. Slice the leek in half, separating the white from the green tops. Clean the green tops under running water and slice very thin. Slice the white part of the leek very thin lengthwise and clean well.

Heat the olive oil in a large sauce pan over high heat and add the green part of the leek. Reduce the heat to medium-high and cook very slowly. Stir frequently.

When the leek is wilted, add the white part of the leek and the diced onion. Reduce the heat to medium and cook for about five minutes, until the onions begin to soften.

Place the rice in the pan with the onions and leeks and stir for about 3 minutes. Add two cups of water, the vegetable stock, sherry, salt and pepper. Cook over medium-high heat stirring frequently. Add the remaining water, 1 cup at a time.

Add the ground paprika and continue cooking. The rice will take about 20 to 25 minutes to cook and may require more water be added. Stir frequently, using about 1/2 cup of water at a time as needed, until the rice is soft but not mushy and there is a small amount of creamy sauce.

Stir in the Parmigiano-Reggiano until it is melted and then gently fold in the diced butternut squash.

Serve.