Mix the butter and the hot milk,until they look somewhat fluffy.

Mix the egg with the sugar in a separate bowl.

Pour the egg and sugar mix over the butter and milk mix. Then,mix again :))

Add the flour over the mix you got at step 3.

Knead the dough and then divide it in two smaller dough "balls" :))

Knead one of the dough balls again,pouring vanilla essence over it.
Knead the other ball using rum essence(or even rum) and cocoa.

Grease a straight surface and "stretch" the two dough balls like seen in the picture. (By the way,what's the actual term for doing that?)

Put the black (thin) piece of dough above the white one and roll them together. Then wrap them in foil and put in fridge for 30 minutes or so.

Get the roll out and cut slices about 1cm thik.
Put them in a baking tray covered in baking paper,and bake them for about 10-12 minutes.
Be careful to leave enough space between the cookies,or else they won't look nice.

Decorate the biscuits if you feel like decorating them. I put melted chocolate on them because they didn't seem sweet enough,but I believe you should try them first before putting chocolate on them.