In a large bowl, combine dry ingredients for dough, stirring to distribute. Create a well in the flour mixture and add warm water (no more than 115° F) and oil.
Stir vigorously until a sticky dough forms and all flour is incorporated.
Turn dough out on to a lightly floured surface. Knead by stretching and folding dough back on itself. Continue for about 5 minutes or 60 turns. Dough should become smoother and fully pull away from the surface, easily forming a ball. *Alternatively: Process dough in a stand mixer with a dough hook for 5-6 minutes.
Oil a large bowl. Roll dough so that it is covered in oil. Cover with a damp cloth or cling wrap. Allow to rise at room temperature until 2 ½ to 3 times the size, about 1 ½ to 2 hours depending on room temperature.
Preheat oven to 425° F. Line a baking sheet with parchment paper.
Turn risen dough out onto parchment paper. Stretch with your fingers to approximately a 9” x 14” rectangle. Cover with a damp cloth or cling wrap and allow to rest for 15-20 minutes.
Slice lemon into extremely thin rounds, less than ⅛th inch. A mandoline is the best tool for this task, but a very sharp knife also works.
Uncover the dough. Use your finger to push dimples into the dough about 2” apart.
Top with thinly sliced lemon, sprinkle with rosemary and flaky salt.
Bake for 12 minutes at 425° F. Reduce heat to 400° F and bake for a further 9-10 minutes until beginning to brown on top. Remove from oven and allow to cool for at least 20 minutes.