For the dough
450g bread flour
7g instant yeast
2 tbsp sugar
1 tsp fine sea salt
30ml olive oil, plus extra for greasing
For the cinnamon sugar
3 1/2 tsp cinnamon
50g caster sugar
50g unsalted butter, melted
For the glaze
6 tbsp icing sugar
1/2 tsp cinnamon
4 tsp whole milk
A pinch of salt
Put the flour, yeast, sugar, and salt in the bowl of a stand mixer, and mix to combine. Make a well in the centre, pour in 360ml lukewarm water and the olive oil, and mix briefly to make a shaggy dough.
Still in the bowl, and using a slightly wet hand, pull one corner of the dough from underneath, stretch and fold it to the centre, then turn the dough 90 degrees. Repeat the stretch, fold and turn three more times.
Cover the bowl with clingfilm or a damp tea towel, and leave to rest for 30 minutes. Repeat the stretch and fold process, let it rest for another 30 minutes, then stretch and fold repeat again.
In a small bowl, mix the cinnamon and sugar. Sprinkle 2/3 of this on top of the dough, then do one more set of stretch and folds. Sprinkle a little more cinnamon sugar on top, then cover the dough and prove for an hour to an hour and a half, until nearly doubled in size.
Generously grease a 30cm x 22cm baking tin with olive oil, then tip in the dough. Using your fingertips, gently stretch out the dough to fill the pan (don’t worry if it springs back), then cover and put in a warm place and leave to rest for another 30 minutes.
Heat the oven to 230C/210C fan/450F/gas 8. Pour the melted butter on to the surface of the dough and sprinkle with the remaining cinnamon sugar. Use your fingertips to dimple the dough, then bake for 20 minutes, until well browned and puffy. Remove from the oven and cool for 10 minutes.
Make the glaze by mixing the icing sugar, cinnamon, milk and salt. Drizzle this generously over the warm focaccia and serve.