I've never heard of bread improver. Is it something I can get at the supermarket?

The recipe I use starts of the yeast with 2 tsp caster sugar and 1/2 cup warm water. Let it froth.

Then you sift 2.5 cups flour, salt together. Add 30g butter and 1/2 cup warm milk. Add yeast mixture. Knead about 10min then rise. Knead again and roll out then roll like a Swiss roll and rise again then bake.