[ For Tart Dough ]
Cream unsalted butter until smooth. Add powdered sugar in 3 batches, and mix well each time. Use an electric mixer to beat on low speed for 2 mins until whitish.

Add beaten egg (room temperature) in 2-3 batches, and beat well each time. Add vanilla oil and mix well.
Sift cake flour over the mixture, and use a spatula to fold to mix until about comes together (large crumble texture).

Gather the dough in the center. Use a spatula to press and spread the dough to stick it to the inside of the bowl. Repeat it two more times. (This will lead to preventing from tearing when you roll it out.) Wrap it with plastic wrap and flatten it. Let it sit in a fridge overnight.

[ For Almond Cream ]
Cream unsalted butter until smooth. Add cinnamon sugar in 2 batches, and mix well each time. Use an electric mixer to beat on low speed for 1 minute.

Add beaten egg (room temperature or more) to the butter mixture in 6-8 batches. Beat it on low speed until smooth thoroughly each time.
(Note: The egg in the almond cream has a ratio that makes it easy to separate, so if the egg is cold, warm it up a little in a hot water bath before adding it.)

Sift ground almonds and flour over the mixture. Use a spatula to mix until smooth. Add brandy and mix well.
Cover it with clingfilm to seal. Let it sit in a fridge overnight.

[ Next day, For Filling ]
Cut sweet potato into bite size.
Put the cut sweet potatoes, granulated sugar, and water in a pot and heat over medium heat. Heat while stirring occasionally.

When the water is almost gone and it has thickened, turn off the heat.
Add butter, and mix gently to coat the potatoes. Add the brandy and mix. Take it out on a tray and spread it. Let it sit to cool.

[ Line the tart pan with pastry. ]
Take the tart dough, and the almond cream out of the fridge. Leave the almond cream at room temperature to soften.

Leave the tart dough for 5-10 mins and use your hands to press it to soften.
Put the dough on parchment paper and flour it. Roll out into 3-4 mm (0.1'') thick. Put it in a freezer for 3-5 mins to harden it a bit.

3-5 minutes later, place it with the pastry side down and peel the paper. Cover the peeled paper again and turn it upside down.
Lightly flour the pastry and rolling pin, wind the dough around a rolling pin and lift.

Place the dough on the pan gently and press it gently into the tart pan. Roll a rolling pin over the pan Trim away any excess.

Poke holes in the bottom with a fork. Use a spatula to soften the almond cream. Put it into the pastry base and flatten. Chill in the fridge for 15-20 minutes.

[ For Crumble Topping ]
While the tart base is chilling, make the crumble topping. Put cut butter, flour, chopped walnuts, and sugar in a bowl. Rub it to make a light breadcrumb texture. Let it sit in a fridge.

[Bake]
Preheat an oven to 200℃ / 392F.
Top the almond cream with well-chilled sweet potatoes, leaving a space on the edge (for crumble topping). Press lightly.
Top the crumble mix along the edge space.

In order to bake the bottom through, put it on a net. Lower the oven to 170 ℃ / 338 and bake for 50-55 minutes.
(Please cover it with aluminum foil for the last 10 minutes if it looks like it will burn.)
Take it out of the oven, and cool it completely. (Freshly baked tart tends to crumble easily, so please remove the tart from the pan after cooling completely.)

[ For Glaze ]
Put water and glaze powder and stir well and heat over low heat. Once boiling, simmer for 2-3 minutes, stirring occasionally. Remove from heat, stir for 1 minute to cool, and strain it.
Brush the top of the sweet potatoes with the glaze.

Remove the tart from the pan. Sprinkle powdered sugar over the top of the crumble.