That's exactly how portals are intended to function. What does one record on the new layout represent, a project?
If so you'll need a relationship between the Projects table and the expenses table:
Projects::ProjectID = Expenses::ProjectID
enable "Allow creation of records in this table via this relationship for the expenses table."
Now a portal on the Projects layout will list all expenses for that Project and you can log new expenses in the portal simply by entering the new data on the blank portal row found at the bottom of the existing portal rows. Each new record is being created in your expenses table so they will also be visible on your expenses layout.
That worked perfectly! Thank you.