Sourdough potato bread

Ingredients

• 150 g potatoes, peeled and cut into pieces (1 cm - see Tips)
• 135 g water, plus extra to spray
• 60 g milk
• 1 tsp caster sugar
• 400 g baker's flour, plus extra to dust
• 1 ½ tsp sea salt
• 1 egg
• 20 g extra virgin olive oil, plus extra to grease
• 200 g Mother sourdough starter (see Tips)