In the bowl of a stand mixer fitted with the dough hook attachment, add bread flour, whole wheat flour, yeast, salt, warm water, and olive oil.

Incorporate on low speed with the dough hook until a homogenous dough forms.

Increase the mixer speed to medium and knead for 5 minutes, or until you can pull a fairly smooth windowpane. The germ and bran in the whole wheat flour will keep it from being perfectly smooth, but there's enough bread flour to allow a nice windowpane. You're still going to perform envelope folds, so don't stress about perfection.

Oil a rimmed half sheet pan (for thinner focaccia) or a 9x13-inch baking pan (for thicker focaccia) with about 1 tablespoon olive oil.

Scrape the dough from the mixer bowl into the oiled pan. Cover with plastic wrap and bulk proof for 30 minutes in a warm spot.

Perform one set of envelope folds by folding each of the 4 corners into the center of the dough, then flip it over onto the seam. This will also conveniently make a square, which will be easier to stretch into a rectangle.

Cover and place the pan back in a warm spot for 15 minutes, then press out by dimpling with your fingers. The goal is to gently stretch the dough towards the edges, nothing more. Cover and rest for another 15 minutes.

Repeat the dimpling and stretching to reach all the edges of the pan. Try to distribute the dough evenly. For a 9x13-inch pan, 2 stretches should be enough to reach the edges. For thinner focaccia on a sheet pan, you may need a third 15-minute interval and one more stretch.

After the dough reaches the edges, drizzle olive oil over the top and dimple by pressing your fingers into the dough until they reach the bottom of the pan. This helps the focaccia retain its dimpled appearance even after proofing and baking.

Cover and place back in a warm spot for 30-45 minutes, or until the dough reaches the top edge of the pan in most places. The dough should look puffy and light. In the final 15 minutes, preheat the oven to 400°F conventional (no fan). Under-leavened dough is the kiss of death for whole wheat bread — it makes it even more dense.

Drizzle on additional olive oil, sprinkle with flaked sea salt, and add any other desired toppings like fresh rosemary.

Bake for 25 minutes in the preheated oven until golden brown on top and bottom.

Remove from the oven, turn out onto a wire rack and let cool slightly before slicing. Serve warm or at room temperature.