In a small bowl, mix dry yeast, a teaspoon of white fine flour and a teaspoon of sugar, then add lukewarm milk and mix everything well again. Leave in a warm place for about 10 minutes to activate the yeast. Put both types of flour and salt in a deep bowl, mix and make a well in the centre to add the activated yeast, lukewarm water and oil.
Stir all ingredients with a spoon until well combined, then move the dough to a floured surface and knead until soft, supple and smooth. Form the dough into a loaf, then transfer it to a bread tin covered with baking paper. Cover it with a kitchen cloth and leave it in a warm place for about 40 minutes to rise.
Gently score the dough with a knife, brush with an egg mixed with some water if desired and sprinkle it with flax and sesame seeds. Bake in a preheated oven at 180ºC for 40 minutes. Allow the bread to cool well before cutting.