BROWN BUTTER

1. Place the butter in a medium saucepan, and place over medium heat. Cook until the butter has melted, and then continue to cook, swirling the pan often, until the butter foams and turns golden brown and nutty - this should take 3-4 minutes.
2. Transfer to a bowl, allow to cool slightly, then transfer the bowl to the freezer and chill the butter until solid. Remove from the freezer and bring to room temperature, stirring often, until soft and spreadable.

BROWN BUTTER SHORTBREAD BASE

1. Preheat the oven to 325°f / 165°c. Grease an 8” (20cm) square pan and line with two pieces of parchment paper that extend over the sides of the pan to use as handles.
2. In a medium bowl, cream together the spreadable brown butter and brown sugar using a spoon or spatula. Add the salt, vanilla, and flour, and bring together to form a soft, homogenous dough. Pat the dough into the bottom of the prepared pan, smoothing down with a flat bottomed measuring cup or offset spatula. Prick all over and chill for 10 minutes.
3. Bake the base for 30 to 35 minutes, until set and evenly golden. Remove from the oven and allow to cool completely.

BROWN BUTTER SALTED CARAMEL FILLING

1. Place the Sweetened Condensed Milk, brown sugar, brown butter and golden syrup in a medium sized heavy bottomed saucepan.
2. Place over a medium heat and stir until melted together, then cook, stirring constantly with a whisk or rubber spatula (I like to use a whisk then switch to the rubber spatula), until the mixture registers 220°f / 105°c on a candy thermometer. Watch the bottom carefully to avoid the mixture catching, turning down the heat if needed.
3. Once the caramel has reached the correct temperature, add the vanilla and salt, mix well to incorporate, and pour it over the cooled shortbread base and smooth off by shaking the pan and using an offset spatula if needed. Transfer to the fridge and allow to set for 1 to 1 1/2 hours or until you can no longer feel heat in it.

CHOCOLATE TOPPING

1. In a heat proof bowl set over a pot of simmering water, melt together the chocolate and the oil, stirring frequently, until smooth. Alternatively, melt together in the microwave in 30 second increments, stirring well after each.
2. Pour over the set caramel filling, and tilt the pan to evenly coat. Bang the pan on the counter several times to smooth out the topping and eliminate any bubbles. If you would like to add the feathering, pipe horizontal stripes of the melted white chocolate across the surface, then feather using a skewer by dragging it up and down the surface of the chocolate, perpendicular to the lines that you piped.
3. Chill in the fridge until completely set, at least an hour or up to overnight. Remove from the pan by using the parchment paper slings. cut into slices using a sharp knife, wiping between each. Store in an airtight container.