The day before, briefly boil milk, 25 g butter and vanilla flavouring. Mix flour and 200 g sugar in a bowl. Add eggs and egg yolk. Add hot milk and mix immediately to a smooth thin dough.
Let it cool down. Stir in rum. Cover the dough and leave to cool for at least 24 hours.
The next day, grease the cannellés baking tin (8 troughs of 75 ml each, see below; alternatively, use a silicone muffin tin) and sprinkle with sugar. Stir the dough, fill the hollows about half to about 1⁄2 cm below the rim.
Bake in a hot oven (electric cooker: 225 °C/circulating air: 200 °C/gas: see manufacturer) for approx. 15 minutes. Turn down the temperature (electric oven: 175 °C/circulating air: 150 °C/gas: see manufacturer) and bake for approx. 1 hour.
Cool the cannellés in the moulds for about 10 minutes, carefully remove them from the moulds and allow them to cool (they may collapse a little). Wash the baking tin and dry well. Bake the remaining dough in the same way.
Wash, clean and halve the strawberries. Mix crème fraîche, vanilla sugar and 2 tablespoons of sugar. Serve cannellés with it. Drink tip: Café au Lait.