Put the butter, icing sugar, egg yolk, and vanilla seeds in a large bowl or food processor. Mix for at least 5 minutes until it is nice and soft and creamy, then put it in a piping bag. Put the raspberries, orange juice, honey, and rose water in a tall measuring cup and blend finely with an immersion blender, then strain.
Now we are going to build: dip 6 cookies in the coulis each time and make a rectangle on a flat surface: a plate, a dish, or a wooden board. Pipe lines of buttercream on top, and repeat again with 6 dipped cookies that you gently but firmly press on top. For the top layer, I used a star-shaped piping tip and piped lengthwise for a neat result, but feel free to get creative.
Let it set for at least 4 hours in the refrigerator. Cut the cake with a warm knife that you dip in boiling water each time and then wipe clean.
Tips
The butter that you use for the Petit Beurre cake is normal dairy butter. You can use vegetable butter if you want to make it vegan, but then you have to omit yolk and find vegan petit beurre cookies. My grandmother always put some alcohol in the cake: rum, eau de vie or cognac. You don't use this if children also go from food ๐