Step 3
Meanwhile, heat the remaining 2 tablespoons oil in a large saucepan over medium heat. Add onion; cook, stirring frequently, until very soft and golden brown, 5 to 8 minutes. Add flour, salt, and pepper; cook, stirring, for 1 minute more. Add milk; cook, stirring and scraping up any brown bits at the bottom of the pan. increase heat to medium-high; cook, stirring until the sauce thickens and bubbles 3 to 5 minutes. Remove from heat.