1. Stir together the yeast and water in the bowl of a stand mixer fitted with the dough hook. Add the flour and mix on low speed until the ingredients are well combined. Mix on medium speed until the dough looks like thick muffin batter, about 2 minutes. 

2. Turn the mixer off and let the mixture sit for 10 minutes to allow the flour to fully hydrate (absorb all the water).

3. Add 2 tbsp (30 grams) of the olive oil, the salt and sugar and then mix on low speed until combined, about 1 minute. 

   Turn the speed up one notch and mix until the dough is quite thick and starting pull away slightly from the sides of the bowl, about 3 minutes. It will be very sticky at this point. 

4. Increase the speed to high and let the dough mix until it comes together, making a slapping noise as it turns, the bowl is clean, and there is a slight sheen to the dough, about 6 minutes. 

5. Stop the mixer and make a window pane test, by pulling off a small portion with floured fingers and stretching it out in all directions. You want to see a thin, nearly transparent film form that you can see light through if you were holding it up to a window. 

   If you can do this without tearing it, then the glutens are well developed and the dough is ready for rising. Add the piece back into the dough and give it a few turns with the machine to work it back in. 

   If it tears, then place it back in with the rest of the dough and continue machine kneading until it passes the test. 

6. Coat the inside of a large bowl with olive oil and transfer the dough to the bowl. Fold the dough over itself several times. and then cover the bowl with plastic wrap or place it in a bag, and let it rise at room temperature until it is 1 1/2 times its original volume, about 2 hours.
7. Generously oil a 12x16 baking sheet. If you only have smaller sheets, then use two, and don't force it to the edges. You will want to make two at no larger than 7x9 or so. 

   Remove the dough from the bowl with oiled hands and press the dough into the pan with your fingers so that it evenly covers the pan. If the dough resists, simply let it rest for 10 minutes and then try again. Keep repeating this till the dough willingly stretches into the corners. 

   Loosely cover the focaccia dough with plastic wrap and let it rest 30 minutes.

8. Preheat the oven to 400F (205C) 

   Uncover the dough. Use your fingers to firmly dimple the surface. Press down until you feel the hard surface of the pan, being careful not to tear the dough. Use a pastry brush to paint the focaccia with 2 tbsp of olive oil and then sprinkle it evenly with about 3/4 teaspoon of salt.

Topping

1. Using a mandolin, very thinly slice the baby potatoes and give them a gentle squeeze to remove any water that developed. Take the drained potato slices and put them in a bowl. 

   To the potatoes add the 1/4 cup olive oil, minced rosemary, and 1 tsp salt. Toss to coat the potatoes evenly, using a rubber spatula. 

2. Spread out the potatoes over the surface of the focaccia, laying them close to each other, even overlapping if necessary. If there is excess watery oil (as the salt may have drawn some more water out of the potatoes), discard this. 

3. Sprinkle the surface with one final 1/2 tsp of salt.

   Take about 3 1/2 oz (100 grams) of the blue cheese and slice into  pieces. Scatter these evenly over the potatoes.

4. Bake the focaccia on the centre rack until it is nicely browned and the underside is crisp, about 30 minutes. Remove the tray to a cooling rack. 
5. Take the remaining blue cheese and cut it into small pieces. Scatter these around the crisped top. The residual heat will melt the cheese into pleasing puddles all over the crisped browned potatoes! 
6. Let the focaccia cool for at least 10 minutes before slicing and serving. 

   Use a good serrated knife to make clean cuts through the potatoes and down into the puffed bread. 

   Store leftovers in an airtight bag at room temperature. Pieces can be reheated at 300F for 8 minutes or so to bring the crunch back!