Preheat the oven to 350°F. Line an 8x8 baking pan with parchment paper, and set aside.
In a medium bowl, beat the butter and sugar until light and fluffy. Add the canned pumpkin, and beat until smooth.
Stir in the flour, salt, and pumpkin pie spice until it's just mixed. Don't overbeat the dough! A little crumbly is fine.
Drop the dough into the prepared 8x8 pan, and press firmly with your hands until it's even and packed. I use the bottom of a measuring cup to get it as level as possible.
Bake for about 20-25 minutes, until the shortbread is a light golden brown. Let it cool for about 15 minutes while you make your caramel.
Combine the sweetened condensed milk, butter, brown sugar, maple syrup, and canned pumpkin in a medium saucepan over medium heat until the mixture is smooth. Attach a candy thermometer to the side of the pan. Bring the mixture to a boil, constantly stirring.
Lower the heat until the mixture is simmering. Continue to stir constantly for about 15 minutes, or until it reaches 225°F and has thickened slightly. Remove the caramel from the heat, and stir in the vanilla extract and salt.
Immediately pour the caramel over the slightly cooled shortbread. Use an offset spatula or butter knife to spread it if you need to. Allow it to cool to room temperature. Alternatively, stick it in the fridge for an hour (or overnight!)
Combine the chocolate and vegetable oil in the top pan of a double boiler. Cook over medium heat, stirring frequently until the chocolate is just melted. (Alternatively, you can melt it in the microwave in 30-second increments). Don't overheat the chocolate!
Pour the chocolate over the caramel layer, using an offset spatula or butter knife to spread it if necessary. Let the chocolate harden, about 30-60 minutes. Cut into 9-12 bars, and sprinkle with flaky salt. Enjoy!