Set yeast mixture aside in a warm place (90-105 degrees) to activate while preparing the other ingredients.
Whisk the arrowroot powder into the warm yeast and water mixture.
Reduce speed to low and stir in the butter powder just until combined and no lumps are left.
Score the top of loaf down the middle and allow to proof in a warm spot (90-105 degrees) for 1 hour.
Score the top of the loaf again and bake in the preheated oven for 35-40 minutes until firm and cooked through.