With the weather turning, we can spend a few more moments in the kitchen, more time discovering new ways of preparing the foods we love most.
Make the crust at least an hour ahead of baking. In a medium bowl, whisk together whole wheat and all purpose flours, sea salt, and sugar. In a separate bowl, whisk egg, sour cream, and lemon juice just until combined.
Cut chilled butter into small pieces and use a pastry cutter or your fingers to mix butter into the dry ingredients until you have a sandy mixture with pea-sized pieces of butter. Add egg and sour cream mixture and continue to mix dough, kneading gently, until it’s smooth and homogenous. Shape into a disk, flatten slightly, wrap with plastic, and place in fridge to chill at least an hour.
While dough chills, place sliced onion in a large frying pan with butter and sea salt. Cook over medium heat for 10-15 minutes, stirring regularly. Once onions are translucent and browned, remove from pan and place in a bowl.
In the same pan, add washed spinach. Cook spinach down, stirring constantly, until it’s reduced and tender. Remove from heat and place in colander. Rinse in cold water, then squeeze all water out of spinach, pressing it a few times to drain properly.
Return caramelized onions to pan and add cooked spinach and a couple pinches of sea salt. Cook over low heat for a few minutes, just to allow flavors to meld. Remove from heat and set aside.
Wash and thinly slice fingerling , about 1/8” thick. Fill frying pan with a couple inches water, and lay potato slices flat in pan—they should be covered in water. Bring to a simmer and cook potatoes until tender when poked with a fork, about 10-15 minutes. Remove from heat, drain in colander, and set aside.
On a lightly floured surface, use a rolling pin to roll out dough into a circle about 1/4” thick. Rough, uneven edges are fine.
Spread the spinach and onion mixture in a circle, starting in the center of the crust, leaving about 2 inches around the perimeter. Sprinkle half the goat cheese over the spinach and onions. Layer potatoes in a concentric circle, starting on the outside and working your way into the center, laying each one slightly over the other as you wind your way in. Drizzle with olive oil, sprinkle with salt and pepper, and sprinkle the remaining goat cheese over the top. Distribute fresh rosemary leaves evenly over potatoes and goat cheese.
Fold in sections of the dough, overlapping as you work your way around. Use your fingers to pinch and seal any open folds so that the dough sits tightly against the galette’s contents. Whisk egg for egg wash, and gently brush egg over the dough to coat.
Bake 35-40 minutes, until potatoes are crisp and browning and pastry is golden brown. Remove from oven and let cool 5-10 minutes before serving.