Here’s what I do now. After I add the paste to my recipe, I line a cookie sheet with waxed paper and put tablespoons of paste onto the sheet. I pop it into the freezer and by the time dinner is over, it has become little frozen blobs of tomato paste. I then put these into a freezer bag, which stays in the freezer until the next time I need a single tablespoonful. Put it frozen into the pot; it will melt and do its job in the recipe.
Or, I suppose you could buy tomato paste in a tube and forget about it. Still, this works for me!