The phrase "last tablespoon" typically means the final bit of something, often referring to the remaining amount in a container or the last portion of something someone has. Full definition
When onions are well browned, add last tablespoon of olive oil and raise heat to high. (treehugger.com)
Such a great way to use those last tablespoons of jams that gather in my fridge, pretty much like the ends of different cheeses... (asaladforallseasons.com)
Drizzle the salad with the last tablespoons of olive oil, lemon juice and extra salt and pepper, if it needs it. (smittenkitchen.com)