Stem and seed the chilies.
In a small sauce pan, cover chilies with water and bring to a boil. Reduce the heat, and simmer, uncovered, for 15 minutes. Remove from the heat, cover, and let the chilies soak for 10 to 15 minutes. drain.
Transfer the chilies to the container of a blender or food processor.
Add the garlic and 1/3 cup water and process until pureed. Set aside.
Melt 1/2 tablespoon of the butter in a small skillet over medium to medium-low heat. Add the almonds and cook, stirring often, until they are golden brown but not burned. Remove from the heat, pour onto a plate, and set aside.
Heat the olive oil and the remaining 1 tablespoon of the butter in a Large pot or Dutch oven, with a good lid, over medium heat. Add the rice and onion, and sauté, stirring frequently, for 5 to 6 minutes. The rice and onions should be starting to turn golden. Turn the heat to between medium and medium high, add the chile purée and stir to combine. Continue cooking, stirring every 30 seconds, for 7 to 10 minutes, or until almost all the moisture has evaporated and the rice no longer sticks together.
Add the stock, milk, salt, oregano, and thyme and stir to combine.
Bring the mixture to a boil, cover, turn the heat to very low, and simmer for 20 minutes. Turn off the heat, stir in the toasted almonds, cover, and let the rice steam, off the heat, for about 15 minutes.
Serve with a dollop of the sour cream and avocado slices if desired.