1. In a medium pot, combine vegetable broth and water, and heat to just under a simmer.
2. In a large, heavy-bottom pot such as a Dutch oven, melt butter in olive oil over medium-high heat.
3. Add leeks to large pot with butter and olive oil, and saute until just beginning to soften, about 3 minutes.
4. Add sliced mushrooms to leeks, and saute about another 3 minutes, until mushrooms begin to give off liquid. Add 1/2 tsp. salt at this point.
5. Add minced garlic and thyme to vegetables, and saute until fragrant, about 30-60 seconds.
6. Add rice to vegetables, and stir to coat rice. Stir frequently, about 1 minute.
7. Reduce heat to medium. Add white wine to rice and vegetables, stirring to release bits from the bottom of the pot. (See note.) Stir until absorbed.
8. Begin adding your heated vegetable broth, 1 cup at a time, to the rice mixture. After each addition, stir frequently to avoid sticking to the pot, and to develop the starches that will make the risotto creamy. The mixture should be at a gentle simmer at this point. Once broth is mostly absorbed, add another cup, and continue stirring - about every 4-5 minutes.
9. After 20 minutes, begin testing the rice for doneness. The grains should be tender all the way through, with no firm bite at the center.
10. Once rice is fully cooked, turn heat to low, add remaining salt and pepper, and parmesan cheese, and stir until cheese is melted. Remove from heat.
11. Serve risotto immediately, as this is when it is at its creamiest.  

Note:

• You can substitute 1/2 cup additional broth or water for the white wine. If you omit the wine, add 1 Tbsp. lemon juice with the broth or water, for acidity.