Heat the oven to 350°F (175°C).
In a saucepan set over medium heat, put the cranberries, sugar, and water. Stir occasionally and cook until every cranberry has burst and the mixture has thickened, roughly 15 minutes. Take off the heat and let it cool.
In another bowl, sift the flour with the salt; reserve.
In a large bowl, cream the butter until smooth. Mix in the brown sugar and vanilla, beating on medium-low until the blend is creamy and even. Then add the flour mixture and beat only until combined, resulting in crumbly clumps rather than a cohesive dough.
Grease an 8x8-inch square pan. Press about two-thirds of the dough evenly into the pan's bottom. Prick lightly with a fork. Bake for 17-18 minutes or until pale golden.
Take out of the oven and spread the cranberry filling evenly over the crust, keeping a 1/4-inch margin from the edges.
With your fingers, break the remaining dough into crumbs and scatter over the filling. Gently press the crumbs into the filling.
Bake for 25-30 minutes, until the top is golden brown.
Remove from the oven and set on a wire rack. While still warm, slice into 16 squares. Let cool completely in the pan.