Do we say "a table spoon OF flour" , "2 litres OF oil" OR
"a table spoon flour"/"2 litres oil"?
You should use "of" in this context.
HOWEVER(!) - in recipe books, when they list the ingredients, they frequently miss out the word "of":
1 tbsp white flour
3 lbs potatoes
This is usually in order to save space on the page and to avoid the constant repetition of the word "of". In a normal sentence, it's important to use the word "of":
I made a delicious cake and it only had one tablespoon of butter, ten grams of sugar and 100 grams of flour.