In a small bowl, whisk together flour and salt and set aside. (If you’re using vanilla powder, stir it into the flour now.) In a large mixing bowl, beat butter and sugar until fluffy and pale. Beat in egg, then vanilla bean paste. Fold in the flour and mix just until combined.
Form dough into a ball, split in 2, then flatten each portion into a disk and wrap in plastic wrap. Chill in the fridge until firm, at least 1 hour or up to 3 days.
Preheat oven to 177°C (350°F) with a rack in the middle of the oven. Line two baking sheets with parchment paper and set aside.
Lightly flour your work surface and rolling pin, then roll out one disk of dough, about 6mm (1/4 inch) thick. Cut out as many cookies as possible and transfer them to a baking sheet, about 2,5cm (1 inch) apart. Bake for 10-12 minutes, until the edges are golden, but the tops remain pale.
As the first batch bakes, gather scraps of dough and form into a disk, chill until firm enough to reroll and make more cookies. Also roll out the second disk of dough, cut out and chill cookies until the first batch is baked. Transfer baked cookies to a cooling rack to cool completely.
Decorate: Put chocolate, coconut oil and a few drops of black food coloring in a heatproof bowl and place it over a saucepan of simmering water. When most of the chocolate is melted, remove the bowl from heat and wipe the bottom with a kitchen towel. Gently stir the chocolate with a whisk. If it’s not dark enough, add more coloring. If it’s not runny enough, add more coconut oil or even boiling water. Because you want the chocolate to be smooth and spreadable, so you can shake off the excess chocolate after dipping.
Take each cookie, dip it into chocolate (top side down), shake off the excess and transfer to a cooling rack. Add the eyes and sprinkles all over the cat’s tail.
Continue with the rest of the cookies. Finally, chill cookies in the fridge until the chocolate hardens. Store covered in the fridge for up to a week.