Oil and line a 900 g (2 lb) loaf tin.
Sift together the polenta, flour, milk powder and salt into a large bowl and stir well to combine. Stir in the yeast, sugar and xanthan gum.
Mix together the eggs, tomato paste and water in a separate bowl, add to the dry ingredients and combine to form a smooth mixture. Beat for 5 minutes, then stir in the remaining ingredients.
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 or it is until brown and sounds hollow when tapped on the bottom. Remove from the oven and transfer to a wire rack to cool.