Soda Cracker Peanut Butter Fudge

2/3 cup milk
2 cups granulated sugar
27 crushed soda crackers (squares)
6 tablespoons peanut butter
1 teaspoon vanilla extract

Bring milk and sugar to a boil, and cook for 4 minutes. Remove from heat and add remaining ingredients. Mix until thick and pour into a 9-inch square pan. Cool and cut into squares.