Preheat oven to 375ºF (190ºC). Grease and line a 9 x 9 inch (23 x 23 centimetre) baking pan with parchment paper, leaving a 2-inch overhang on the sides (for easy unmolding).

In the large bowl of a stand mixer, beat the butter with the Redpath® Granulated Sugar, pure vanilla extract, and salt until light and fluffy.

Sift the flour over the butter mixture. Using a wooden spoon, incorporate the flour into the butter mixture until just combined. The mixture will be crumbly; use your hands to knead a few times until the dough comes together in a ball.

Press the shortbread dough into the prepared pan in an even layer. Refrigerate until the shortbread is set; about 30 minutes.

Bake until the shortbread is light golden; about 20 to 25 minutes. The shortbread may be under baked at this point, but that is fine since it will be baked longer with the topping. Remove from the oven and allow to cool slightly.

Combine the Redpath® Dark Brown Sugar, heavy cream, and butter in a heavy-bottomed saucepan. Set over medium heat and stir with a wooden spoon until the butter is melted and the mixture has come to a simmer.

Continue to simmer without stirring until the sugar is dissolved and the mixture is bubbling; about 5 minutes.

Add the vanilla extract and salt; stir to combine. Stir in three-quarters of the pistachios until coated and spread on top of the shortbread base in an even layer. Sprinkle the remaining pistachios on top. (how to 3)

Bake until the topping is just set; about 8 to 10 minutes.

Allow to cool completely in the pan on a rack.

Before cutting the bars, run a knife around the edges of the pan to loosen. Lift out of the pan to a cutting board and cut into bars.