Preheat the oven to 350° F and grease an 8" x 2" tart ring with cooking spray or melted butter.

Place the softened butter and vanilla extract into a stand mixer bowl equipped with a paddle attachment, turn the mixer to medium speed and mix until the butter is light and airy. Next, add the powdered sugar, and mix until well combined. Then add the egg and continue to mix.

Turn off the mixer, and scrape down the sides of the bowl with a rubber spatula, ensuring the egg is fully incorporated. Turn the mixer back on low speed and incorporate the sifted flour.

Continue to mix until there are no more flour streaks.

Mix enough to just put the dough together, then move it to a lightly floured surface. Using both hands, create a 2" thick ball, then cover it with plastic wrap.

Place the dough in the refrigerator for an hour.

After rest, unwrap the dough and place it back on a floured surface. Using a rolling pin, roll the dough outward, starting from the center to the edges. Continue rolling until you obtain a 1/4 of inch disc. If the dough gets too warm and challenging to handle, you can roll it between sheets of parchment paper.

Cut the dough into a circle using the tart ring; this will be your crust bottom. With the help of an offset spatula, move the circle to a baking tray lined with a baking mat. Then use a sharp knife to cut a long strip that will serve as the tart edges. Place the strip into the tart ring and, applying pressure with your fingertips, push the dough against the sides of the ring, ensuring there is no space in between.

Trim the crust edges with a sharp knife, then pierce holes in the bottom using a fork, preventing the crust from inflating in the oven.

Place the tart crust in the freezer for 15 minutes, then bake in a 350°F preheated oven for 15 minutes or until the edges are fully set.

Remove the tart shell from the oven and place it on the counter using oven gloves. Lightly beat one egg yolk with a fork and brush the tart surface with it.

Return the tart to the oven and bake for another 15 minutes or until golden. Remove it from the oven and place it on a wire rack to cool off.

Chop the dark chocolate and place it into a medium bowl. Meanwhile, place the heavy cream and honey in the saucepan and bring to a simmer.

Pour the heavy cream on the chopped chocolate, add the rum and mix it using a rubber spatula until completely melted. When the ganache reaches 100°F (check this using a kitchen thermometer), add the cold butter cut into cubes, and mix again.

Pour the chocolate mixture into the shortbread crust, then place it into the refrigerator for at least 4 hours or until the ganache filling sets.

Rehydrate the gelatin powder in water in a small bowl for 5 minutes. In another small bowl, mix cocoa powder and granulated sugar.

Place water and heavy cream in a small saucepan and bring it to a simmer, then add the cocoa/sugar mixture, mix, and let simmer until dissolved. Remove the pan from the heat.

Add the gelatine to the saucepan. Mix until completely melted, then strain it to remove any clumps.

When the glaze reaches 90°F (using a kitchen thermometer to check), pour it on the tart top; holding the tart with both hands, gently tilt the tart to allow the glaze to spread out evenly across the surface. Afterward, place it in the refrigerator for a couple of hours.

To cut perfect slices, prepare a container with hot water, dip the knife in hot water, wipe it dry, and quickly cut a piece. To make all the portions neat, clean the blade, dip it in hot water, wipe it dry and continue to repeat the process after each cut.

Serve the sliced tart with a scoop of vanilla ice cream, fresh berries, or chocolate shavings.