BigOven remembers links over time. I'm not sure which version you downloaded, but for the past year or so, "Sugar" has been one of the pre-populated links. Regardless, it's really simple to define it once, and then BigOven will remember it for you.
What I did was:
1) Launched BigOven
2) Clicked "New" on the toolbar to create a new recipe. I called it "Test Recipe".
3) Clicked on the Edit tab. Changed serving size to 16 servings for this recipe.
3) Enter the following for the first ingredient on the "add" line:
2 <Tab> cups <tab> Sugar <enter>
BigOven adds the ingredient line and turns it orange. If it didn't simply double-click on the ingredient line marker (the scale icon for that line) and match it up with "SUGARS, GRANULATED". If you entered the quantity and units in the right fields, BigOven should recognize that it's 2 cups and be ready to link. Click the link button. (You may have to then force a save/commit by, for example, moving to another recipe and then coming back to it), and then you can view the Nutrition tab for the Test recipe you entered. It'll show 97 calories for the recipe.