That legend is only partially true. In the first-season episode "The Potato Show," Julia was making four potato recipes. One was "Pommes de terre Byron," or a pancake made from the flesh of baked potatoes mixed with butter, cream and other ingredients. She was browning it in a pan, and then attempted to flip it although (as she soon realized) it hadn't sufficiently browned on the bottom. As a result, half the potato mixture from the pan ended up on the stovetop. She quickly scooped it back into the pan, and joked "Remember, you are alone in the kitchen and nobody can see you." She later successfully flipped another pancake (this time made from grated raw potatoes mixed with cream cheese and eggs), and encouraged viewers to practice flipping.
Later, a story arose that she dropped a roast, or a chicken, or a turkey, or some other item, then simply dusted it off, put it back on the plate, and said, "You're alone in the kitchen!" Some people claim to remember seeing this themselves. However, fans of the show have reviewed all episodes and found that nothing of the sort ever happened; the potato-pancake gaffe was the only time she dropped something and put it back in the pan.
The same can be said of the story of her drinking wine directly from the bottle: although some claim to have actually seen it happen, it actually didn't, as a review of the episodes has found.
These stories seem to be the result of "manufactured memories" and from confusing spoofs of Julia's show and style with her real show and persona.