In a skillet over medium heat, melt the butter and add the diced white onion. Sauté until the onions become translucent, about 3-4 minutes. Stir in the ground chuck, breaking it up with a spatula, and cook until browned. Season with salt and freshly ground black pepper. Once cooked, sprinkle the flour over the meat mixture and stir to combine.
Gradually pour in the milk while stirring continuously to avoid lumps. Cook until the mixture thickens, then fold in the diced green chilies and 3/4 cup of chopped white onion. Remove from heat and set aside.
In another skillet, heat vegetable oil over medium-high heat. Once hot, carefully add the flour tortillas one at a time, frying until they turn golden brown and crispy. Drain on paper towels to remove excess oil.
On each fried tortilla, spread a generous amount of the creamy filling. Top with shredded cheddar cheese and any additional toppings of your choice. If you like it spicy, drizzle with picante sauce.
Preheat your oven to 400°F (200°C). Place the assembled pizzas on a baking sheet and bake for about 10-12 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let cool for a few minutes before serving. Slice into wedges and enjoy your Taco Villa Things with friends and family!