Heat a 3-4 quart saucepan over medium-high heat. Add 2 tablespoons of butter and allow it to melt. When the foaming subsides, add the shallots. Cook, stirring often, for about 5-7 minutes. Once softened, add the quinoa. Cook, stirring constantly, allowing any of the excess water to evaporate.
The quinoa should start to toast a little bit and dry out. Add the white wine and stir well. Allow the wine to cook down and almost evaporate.
Add 2 cups of the vegetable stock and lower heat to a simmer. Cook, uncovered, for 5-10 minutes, or until all of the liquid has been absorbed. Stir every so often.
Add another cup of vegetable stock, stir a few times, and let cook for another 5-10 minutes.
Once that liquid has been absorbed, add the remaining 1 cup stock plus the pumpkin puree. Stir again and let cook, uncovered, until all of the liquid is absorbed. Add more stock if needed. The quinoa should be cooked through completely.
Stir in the cheese a little at a time, stirring very well between additions. Taste and add salt and pepper, if needed.
While quinoa is cooking, heat a large skillet over medium-high heat. Add the remaining 2 tablespoons of butter and allow to melt. Add the sliced mushrooms and season well with salt and pepper. Cook, stirring often, until the mushrooms start to brown. Add 2 tablespoons of the fresh sage and stir well. Continue cooking until mushrooms are nicely browned and fragrant. Add the remaining 1/2 cup of wine and scrape up the browned bits on the bottom of the pan. Remove from heat, but keep warm until ready to serve.
To serve, divide the quinoa risotto between 4 wide bowls. Top each with some of the sautéed mushrooms and garnish with a little of the remaining fresh sage and parmesan cheese. Serve immediately.