Toasted-Flour Sablés

Place a rack in middle of oven and preheat to 450°F. Sprinkle flour evenly over a rimmed baking sheet and toast, stirring often once top layer of flour browns, until all flour is golden, 10–15 minutes (flour will burn quickly, so check often). Let cool, then sift into a medium bowl and whisk in egg yolks and salt.
Using an electric mixer on medium speed, beat butter and sugar in a medium bowl, until pale and fluffy, about 5 minutes. Reduce speed to low and add flour mixture plus 2 Tbsp. water; mix just until combined (mixture will look crumbly but will hold together when pinched). Transfer dough to a sheet of parchment paper and form into a 12" log. Tightly roll up in parchment, then wrap tightly in plastic. Chill until firm, at least 4 hours.
Preheat oven to 400°F. Slice a little dough from both ends of log to square off; unwrap and slice dough 1/4" thick. Place on rounds on parchment-lined baking sheets, spacing about 1" apart. Bake cookies, rotating baking sheets halfway through, until edges are golden but centers are still pale, 10–12 minutes. Let cookies cool on baking sheets 5 minutes, then transfer to wire racks and let cool completely.
Dough can be made 1 day ahead. Keep chilled, or freeze up to 1 month.