1. In a medium saucepan, bring the chicken broth to a simmer; reduce heat to low and keep warm.
2. Melt the butter in a large skillet over medium-low heat. Add the onion; saute until softened, 3 minutes. Add 1 teaspoon of the garlic; saute 30 seconds. Stir in the rice, then add 1/2 cup of the sherry; cook until absorbed, stirring frequently, about 2 minutes. Add 1/2 cup of the broth, stirring until absorbed, 2 minutes. Add remaining broth 1/2 cup at a time; stir each 1/2 cup until absorbed before adding the next. Cook, stirring frequently, until rice is tender and creamy, 20 to 25 minutes.
3. Heat 2 teaspoons of the olive oil in a nonstick skillet over medium-high heat. Add the mushrooms and saute until golden, 5 to 7 minutes. Add 1 teaspoon each of the garlic and thyme and the pinch of salt; saute 1 minute and transfer to a plate. Add remaining oil and the shrimp to empty pan; cook 2 minutes. Add remaining garlic and saute 1 minute more. Add remaining sherry and simmer 1 minute, until shrimp are just barely cooked through; set aside.
4. When the risotto has finished cooking, stir in shrimp and liquid, mushrooms, Parmesan, parsley and remaining thyme. Warm 2 minutes. Spoon into bowls and serve.