Preheat oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.

Heat olive oil in a large skillet over medium heat. Add onion and cook until softened, about 4-5 minutes. Add garlic and cook for 1 minute more.

Add the shrimp to the skillet, season with salt and pepper, and cook until just pink and opaque (about 2-3 minutes). Remove from heat and stir in cilantro. Set aside.

In a medium saucepan, melt butter over medium heat. Whisk in flour and cook for 1 minute, stirring constantly.

Gradually whisk in the milk until the mixture is smooth. Bring to a simmer and cook until thickened, about 2-3 minutes.

Remove the sauce from the heat. Stir in the sour cream, diced green chiles, and cumin. Add 2 cups of the shredded cheese, a handful at a time, stirring until melted and smooth. Season with salt and pepper to taste.

Spread ½ cup of the sauce on the bottom of the prepared baking dish.

Divide the shrimp mixture among the tortillas, roll them up, and place them seam-side down in the dish.

Pour the remaining sauce over the enchiladas, covering them completely. Sprinkle with the remaining 1 cup of cheese.

Bake for 20-25 minutes, until the sauce is bubbly and the cheese is melted.

Let rest for 5-10 minutes before serving. Garnish with additional cilantro if desired.