Start by melting the butter in a medium-sized saucepan over medium heat. Once melted and bubbling, whisk in the flour to form a roux. Continue whisking for about 1-2 minutes until the roux takes on a light golden color. This step is crucial as it helps thicken the sauce and adds depth of flavor.

Add the chopped onion and minced garlic to the roux. Sauté until the onion becomes soft and translucent, which should take about 3-4 minutes. The garlic will start to release its fragrant aroma, making your kitchen smell fantastic.

Stir in the chopped roasted green chiles. Let them cook with the onion and garlic for about 2 minutes. This will allow the flavors to meld together beautifully.

Slowly pour in the chicken or vegetable broth while whisking continuously. This will prevent any lumps from forming and help integrate the roux with the broth. Bring the mixture to a simmer and let it cook until the sauce starts to thicken, approximately 5-7 minutes.

Mix in the ground cumin, a pinch of oregano, and salt. Continue to simmer for another 5 minutes, stirring occasionally. If the sauce becomes too thick, you can adjust the consistency by adding a bit more broth.

For a smoother texture, use an immersion blender to puree the sauce until it's completely smooth. Alternatively, transfer it to a regular blender and blend until creamy. This step is optional but recommended for a velvety texture.

Taste the sauce and adjust the seasoning if necessary. You might find that extra salt or cumin could enhance the flavor even further.