Combine flour, powdered sugar, cocoa powder, salt, and granulated sugar in a bowl.
Cut in cold butter until mixture resembles coarse crumbs.
Add cold egg and mix until dough forms.
Wrap dough and chill for 30 minutes.
Roll out dough and line tart molds, then chill for 15 minutes.
Bake at 350°F (175°C) for 15 to 18 minutes until set and cooled completely.
For raspberry jam, heat raspberries and sugar in a small saucepan.
Mix pectin with a little sugar, add to raspberries, and cook 2 to 3 minutes until thickened.
Blend jam if desired and let cool.
Heat milk and heavy cream until warm, then add white chocolate and stir until melted.
Mix in black sesame paste and salt, stir in bloomed gelatin until dissolved, then cool slightly.
Fold in whipped cream gently until smooth and airy.
For brandy snaps, melt butter, brown sugar, and corn syrup in a saucepan.
Remove from heat, stir in brandy (optional), flour, salt, and toasted sesame seeds.
Spoon small circles of batter onto parchment paper and bake at 355°F (180°C) for 6 to 8 minutes.
Let brandy snaps cool until crisp.
Assemble tarts by spreading raspberry jam in tart shells, then topping with black sesame mousse.
Arrange fresh raspberries on mousse and garnish with brandy snap pieces.