Some context is in order. Scout beat up Walter Cunningham on the first day of school, because she got in trouble trying to explain to Miss Caroline why Walter did not have lunch and why it was a bad idea to offer Walter a quarter to buy some lunch.
When Scout had Walter's nose in the dirt, Jem came over and broke up the fight. In addition, Jem invited Walter to have dinner at their house. Initially, Scout did not like the idea, but she grew to accept it. She even said that she would not beat him up again. She also mentioned the fact that Calpurnia was a great cook. Here is the quote:
“I wouldn’t be too certain of that,” I said. Jem’s free dispensation of my pledge irked me, but precious noontime minutes were ticking away. “Yeah Walter, I won’t jump on you again. Don’t you like butterbeans? Our Cal’s a real good cook.”
In conclusion, Scout tries to repay Walter by inviting him for dinner.