In heatproof medium bowl, add chipotle pepper and ancho pepper. Pour enough hot water to cover and let soak for 15 minutes or until softened. Reserve 1/4 cup soaking liquid; drain peppers.
In large skillet set over medium heat, melt butter. Add onion and garlic; cook, stirring occasionally, for 3 to 5 minutes or until starting to soften. Transfer to blender (reserve skillet).
Add rehydrated peppers and reserved soaking liquid to blender. Add tomatoes and salt; purée until smooth.
Transfer tomatoes mixture to reserved skillet and bring to a simmer over medium-high heat. Cook, stirring occasionally, for 8 to 10 minutes or until sauce has thickened and flavors are married.
Add shrimp to skillet; cook, stirring occasionally, for 3 to 4 minutes or until shrimp turn pink and curl and are cooked through.
Meanwhile, prepare rice according to package directions.
Serve spicy shrimp mixture over rice. Garnish with cilantro.
Serve with squeeze of lime juice, drizzle of sour cream or crumbled cotija cheese if desired.