Put milk, butter and coffee powder in a pot and bring to the boil briefly. Remove milk from the stove. Mix flour and 200 g sugar in a bowl. Add eggs and egg yolks. Pour in hot milk and mix immediately with the whisk of the hand mixer to a smooth, thin dough. Let the dough cool down, stir in rum. Cover and chill for at least 12 hours.
Stir the dough once again and fill in portions up to approx. 5 mm below the rim into the non-greased silicone mould (18 wells; approx. 50 ml each). Bake cannellés in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 30-40 minutes. The cannellés should be well browned. If they "swell" out of the tin, press back carefully
Remove the cakes and let them cool on a cake rack for about 10 minutes. Carefully remove cannellés from the individual hollows and let them cool completely. Some cannellés collapse a little. Wash the tin, dry and process and bake the remaining dough in the same way
waiting time approx. 12 1/2 hours