Towards the end of the baking time, start making the caramel/almond topping. In a medium-size microwave-safe measuring cup or bowl, combine the cream, honey, vanilla and butter. Microwave on high power for 2 minutes. Set aside.
In a heavy medium-sized saucepan, combine the sugar, water and corn syrup and water and bring to a boil over moderately high heat, stirring just to combine. Don’t stir after this.
Cook the syrup over moderately high heat, swirling the pan occasionally, until a medium amber caramel forms, about 8-10 minutes. (Watch the syrup carefully the last couple minutes, swirling the pan more frequently at this point to prevent burning). Remove from the heat.
Carefully add the honey/cream mixture (it will bubble furiously) and stir to combine. Return the pan to the burner and cook the caramel over moderately high heat, stirring frequently until a candy thermometer registers 255°, about 7-10 minutes. Stir in the almonds and immediately pour the caramel mixture over the shortbread, spreading to an even layer.
Return the pan to the oven and bake for 7-10 minutes, or until the topping is bubbling all over and a nice deep golden brown. Transfer the pan to a cooling rack and sprinkle with flaky sea salt, if desired. Allow to cool completely before cutting. I like to allow at least 2 hours.
Run a thin-bladed knife along the two edges of the pan that do not have parchment to loosen the shortbread. Pull up on the parchment paper and transfer the shortbread to a cutting board. Using a sharp, heavy knife, cut the pastry into desired size squares.