The side of an oven-baked pancake (sometimes referred to as a "Dutch Baby" or "German Pancake") tends to brown before the inside is fully done due to differences in heat transfer and cooking dynamics within the pancake batter.
When you pour the pancake batter into a preheated oven-safe skillet or baking dish, the heat from the oven immediately begins to cook the outer edges and the bottom of the pancake. The direct contact with the hot surface of the skillet causes those areas to brown and set quickly.
In contrast, the center of the pancake is surrounded by batter and is not in direct contact with the hot surface of the pan. As a result, it takes more time for the heat to reach the center and cook it thoroughly. During this time, the outer edges continue to cook and brown, creating the characteristic contrast between the nicely browned sides and the still cooking center.
To achieve a more even cooking and browning, some people recommend rotating the skillet or baking dish halfway through the cooking process. This helps to ensure that the pancake cooks more evenly and prevents one side from getting too browned before the other side has a chance to catch up.
Additionally, oven temperatures and the thickness of the pancake can also influence the browning pattern. If you find that the sides brown too quickly, you can experiment with lowering the oven temperature slightly or adjusting the thickness of the batter to see if that helps create a more even result.