Step 1

Heat butter and olive oil in a small saucepan over medium heat; cook and stir onion and garlic until tender and fragrant, about 1 minute. Add flour and whisk until flour is lightly browned and onion is translucent, 2 to 3 minutes.

Step 2

Mix milk, Parmesan cheese, basil, oregano, salt, and black pepper into onion mixture. Cook, whisking continuously, until cheese is melted and sauce has thickened slightly, about 5 minutes. Remove from heat.