In a large Dutch oven, heat olive oil over medium heat until shimmering. Add onion (along with carrot and celery, if using) and cook until soft and golden around the edges. Add garlic and cook about 30 seconds.
Add rice and continue to cook until the lighter colored rice becomes opaque.
Add in water or broth and season with salt and pepper. Stir well to combine.
Cover and reduce heat to low. Cook rice for 45 to 55 minutes until very little steam is escaping the pan. Remove from heat and let sit for 15 minutes.
For the mushrooms, melt butter in a fry pan until bubbly, add mushrooms and cook, stirring occasionally until browned. If desired, add 2 to 3 tablespoons of white wine and continue to cook until evaporated.
Uncover rice and fluff with a fork. Mix in mushrooms, almonds and fresh herbs, as desired.
Let sit another 5 minutes and serve.
Notes
Different rice blends require different amounts of liquid, adjust the amount according to the package instructions. For a more neutral, cleaner taste use water. For a more savory and complex flavor, use vegetable or chicken broth. If using broth, adjust the amount of salt as necessary.