Grease and line a 1 kg (2 lb) loaf tin. Sift the polenta, flour, milk powder and salt into a large bowl and stir well to combine. Stir in the yeast, sugar and xanthan gum.
Place the eggs, herbs and measurement water in a bowl and mix together. Stir this mixture into the dry ingredients and combine to form a soft dough. Beat for 5 minutes, then stir in the feta cheese.
Spoon the mixture into the prepared tin, cover with a clean damp tea towel and leave in a warm place to rise for about 30 minutes, until the mixture is near the top of the tin. Place in a preheated oven, 180°C (350°F), Gas Mark 4, for about 45 minutes until brown and hollow-sounding when tapped.
Remove the loaf from the oven and transfer to a wire rack to cool.