As the song says, "A spoonfull of sugar makes the medicine go down." There was also a singing group called "The Loving Spoonfull" at one time. Americans do say "sugar spoon" for a spoon placed in a sugar bowl for scooping the sugar. In the sentence under discussion we would most likely say "spoonfull of sugar" rather than "spoon of sugar." Recipes call for a "teaspoon of sugar" or a "tablespoon of sugar" but a "spoon of sugar" sounds a little strange.