Heat 280ml water in a saucepan for a minute until warm but not too hot to stick your finger in (don’t burn yourself!). Remove from the heat, then add 50g butter. Combine the flour, yeast, sugar and 1 tsp salt in a large bowl or a tabletop mixer. Add the warm water and beat to make a soft dough. Knead for 10 mins by hand, or 5 mins in a mixer, until the dough feels stretchy and smooth. Tip into a clean, oiled bowl and cover with oiled cling film. Leave to rise for 1½-2 hrs, or until doubled in size.
Brush a large baking tray with oil and scatter over the polenta. Knock the air out of the dough. Pinch off small pieces (about the size of a walnut), then roll each piece into a ball and put on the baking tray. Leave a little space between each dough ball.
Heat oven to 180C/160C fan/gas 4. Cover the tray with oiled cling film, then prove for 30 mins-1 hr until the dough has doubled in size and the balls are touching. Mix the remaining butter with the garlic. When the rolls are ready to cook, brush the tops with the garlic butter and scatter with the cheeses. Bake for 25-30 mins until the dough balls are cooked through. Leave to cool for 5 mins, then serve.