Start by preheating your oven to 350ºF. 

Make the sour cream enchilada sauce: add the butter and olive oil to a skillet over medium heat and allow the butter to melt. Once the butter is melted, sprinkle the flour into the skillet and stir it in with a whisk.

Continue stirring the flour around for 1-2 minutes to let the flour absorb all of the fat, and to cook off the flour taste. Now gently pour in the chicken broth while whisking vigorously. Keep whisking until a roux is formed and the mixture is smooth and thickened. 

Add about 1-2 tablespoons of the hot roux to your sour cream and mix it in with a spoon. This is to bring the sour cream up to temperature so that it does not curdle when you add it into the hot roux. 

Once the sour cream is tempered, add it into the roux, and mix it until it is completely combined. If the roux gets too thick, add a bit more chicken broth until you get your desired consistency, (you want a gravy-like consistency). 

Add in all of your seasonings, including the adobo seasoning, cumin, garlic powder, and black pepper, and mix them until they are fully combined. Taste the sauce and add salt if needed. Remove the sauce from the heat. 

Assemble the enchiladas: Combine the shredded chicken, diced onion, sour cream enchilada sauce, Monterey jack cheese, cumin, garlic powder, and salt in a bowl and mix it together. 

Grease a 9x13 inch baking dish and add about ¼ to ½ cup of the enchilada sauce to the bottom of the dish. Now scoop about 2 tablespoons of the chicken mixture into the center of each tortilla and roll it up tight, then place it into the baking dish. 

Continue rolling each enchilada until you have used all of the chicken mixture and flour tortillas. Then pour the sour cream enchilada sauce evenly over the top of the enchiladas, and use a spoon to spread it out to make sure they are all evenly covered. 

Sprinkle the rest of the monterey jack cheese on top of the enchiladas. Cover the dish with foil and place it in the oven to bake for about 20 minutes, or until the cheese is melted. Garnish with chopped cilantro if desired. And enjoy!