Preheat the oven to 350°F (175°C). In a mixing bowl, combine flour, sugar, melted butter, and salt. Mix until crumbly.

Press the mixture into the bottom of a greased 9x9 inch baking pan.

Bake for 10 minutes, then remove from the oven.

In another bowl, combine sliced nectarines, sugar, lemon juice, cornstarch, and vanilla extract. Mix well.

Spread the nectarine mixture evenly over the pre-baked crust.

Return the pan to the oven and bake for an additional 20 minutes, or until the filling is bubbly and the edges are golden.

Allow to cool completely before cutting into bars.