Whole Wheat Cheddar Onion Focaccia

Steps

1. In a large bowl, stir the lukewarm water, honey and instant yeast together. Add the whole wheat flour and the bread flour and mix until no dry patches remain. Cover and rest 20 minutes so the whole wheat bran softens.
2. Sprinkle the salt over the dough and add one fifth of the olive oil (about 2 teaspoons). Squeeze and fold in the bowl for 3 to 4 minutes until smooth and stretchy. This is about 80% hydration and 2% salt.
3. Scatter half of the cheddar over the dough and fold it in until evenly spread. Cover and let rise at about 75°F (24°C) for 1 hour, giving the dough two sets of stretch-and-folds 20 and 40 minutes in. It should look puffy and nearly doubled.
4. While the dough rises, warm another fifth of the olive oil in a skillet over medium-low heat. Cook the onion with the black pepper, stirring often, for 20 to 25 minutes until soft and golden. Stir in the mustard and let cool.
5. Brush a 9-by-13-inch pan with another two fifths of the olive oil. Turn the dough into the pan and gently stretch it toward the corners; if it springs back, rest 10 minutes and stretch again.
6. Cover and proof at about 75°F (24°C) for 45 to 60 minutes, until puffy, jiggly and it springs back slowly when poked. Meanwhile, preheat the oven to 425°F (220°C).
7. Drizzle the remaining fifth of the olive oil over the dough and press deep dimples with oiled fingertips. Scatter the cooled onions over the top, then the remaining half of the cheddar.
8. Bake 22 to 26 minutes, until golden and the center reads 200°F (93°C). Cover loosely with foil for the last 5 minutes if the cheese browns too fast.
9. Lift the focaccia onto a rack and cool at least 30 minutes before cutting into 12 slices; covering it with a towel while it cools keeps the crust soft.