Why do butter tarts sink drastically when baked?

- Too much heat: Baking the butter tarts at a high temperature or for too long can cause the filling to overcook and shrink, resulting in a sunken appearance.

- Incorrect filling consistency: If the filling is too runny before baking, it will continue to spread and lose its shape in the oven, leading to a sunken appearance.

- Overmixing the crust: Overmixing the butter tart crust can result in a glutenous crust, leading it to shrink too much during baking and pulling the filling down.

- Not chilling the dough: Refrigerating the pastry dough before rolling and filling helps firm it up and prevent excessive shrinking during baking.

- Leavened dough: If you accidentally used a leavened dough, like yeasted dough, for the butter tarts, the baking powder or yeast will cause the tarts to rise and then deflate, resulting in sunken centers.

- Old fillings: Freshly prepared butter tart filling is recommended for the best texture. Old fillings might not hold their shape as well and may lead to sinking.

- Too much filling: Overfilling the butter tart shells with the filling can cause the filling to spill over and sink during baking.

- Uneven filling: Unevenly distributed fillings can cause certain parts of the butter tarts to sink when denser fillings settle during baking.

To prevent butter tarts from sinking while baking, try the following tips:

- Bake at the right temperature: Follow the recipe's recommended temperature, and avoid over-baking.

- Chill the dough before baking: This helps prevent excessive shrinking of the crust.

- Use the correct filling consistency: The filling should be thick and spreadable, not runny or too thin.

- Don't overmix the crust: Mix the dough only until it comes together to avoid a glutenous crust.

- Use fresh fillings: Old fillings may not hold their shape as well and may contribute to sinking.

- Don't overfill the tart shells: Leave enough room in the shells to prevent the filling from overflowing.

By following these tips, you can greatly reduce the chances of your butter tarts sinking while baking.