Line a 9x9 inch square pan with two pieces of parchment paper, creating a sling for easy removal.

In a medium bowl, cream the butter until smooth, then add the powdered sugar and beat for 2 more minutes.

Fold in the flour, salt, and vanilla until just combined.

Press the dough into the prepared pan and use the back of a spoon or small measuring cup to pack it in and level it out. Prick the dough with a fork all over and place in the fridge to chill for 30 minutes.

While the base is chilling, preheat the oven to 325 degrees F. Bake the shortbread for 30-35 minutes or until the edges are golden brown. Allow to cool completely before pouring the caramel on top. 

Start by making the brown butter. Heat the butter in a saucepan over medium heat until the fat solids separate and the liquid turns an amber color. Swirl the butter while it browns to ensure even cooking. Pour into a bowl to cool before making the caramel filling. You can also place it in the fridge to chill it faster.

Once the brown butter is room temp, place it in a saucepan with the brown sugar, sweetened condensed milk, and light corn syrup.

Heat over medium heat, whisking constantly until it reaches 235 degrees F.

Remove from heat and stir in the salt and vanilla.

Pour caramel over the cooled shortbread base. Chill the bars in the fridge for at least two hours or overnight. 

Once chilled and set, cut into 22 long bars or 44 short bars. I cut the solid block down the middle, then cut 11 long bars from each block. Place cut bars in the freezer while you melt the chocolate.

Combine chocolate and oil in a small bowl and place over a double boiler. Alternatively, you can heat the chocolate in the microwave in 20 second intervals.

Once melted, take half of the bars out and coat them in the chocolate. Place on a wire rack over a sheet pan to set.

Once set, place back in the fridge or freezer. Repeat with the remaining bars. 

For the chocolate drizzle, melt the other chocolate and place in a piping bag. Snip the end of the bag and quickly drizzle over the ends of each bar.

Sprinkle with flaky sea salt if desired.

Place back in the fridge or freezer until ready to be served.