"Extra filling" means having more than what is typically expected or necessary, especially when referring to food or a filling in a sandwich or pastry. Full definition
Once the tight areas and corners are perfect, you can now start adding small amounts of extra filling as you work your way towards the seam opening. (pillowtip.com)
* Depending on the size of the shooter glasses you use, you may have extra filling left over. (brighteyedbaker.com)
I did notice that to fill all the mini pies (recipe makes about 12 - 14) you need extra filling sauce and less apples. (browneyedbaker.com)