Put the milk, butter and water in a pan and gently heat until the butter is melted. Set aside to cool until just warm.
When the milk and water mixture is just warm, so you can put your finger into it place the fresh yeast into it and allow to dissolve. If using dried yeast add it directly to the dry ingredients
Tip the flour, sugar, and salt into a large bowl and gradually work in the milk mixture, then the egg, until you have a smooth dough. Tip the dough onto a floured surface or into a stand mixer fitted with a dough hook and knead until elastic and shiny. Divide into 24 (about 80g each) pieces and roll into tight balls. Transfer to baking trays lined with baking parchment, leaving plenty of space between them, and put in a warm place to prove for 30-45 mins.
Heat oven to 200C/180C fan/gas 6. Press the rolls down gently using your hands, then brush over some milk and scatter over the sesame seeds, if you like (or, dust with some flour). Bake for 10-12 mins until risen and lightly golden. Leave to cool completely, then serve. Make up to two days ahead and keep in an airtight container or freeze.