In the medium bowl, whisk together the flour, baking powder, and salt. In the bowl of the stand mixer, beat together the sugar, butter, and vanilla until fluffy. Add the yolks one at a time, beating after each. Then add the flour mixture and mix on medium low until all the ingredients are fully incorporated.
Roll the dough into a 12″-long cylinder. Cut the cylinder into 3 pieces and then roll each into another 12″-long cylinder. Slice each cylinder into twelve 1″-long pieces. Roll each into a ball and place on the lined baking sheets, arranging them about 2 inches apart. Flatten each ball into a small disk, then use your finger to poke a hole in center of each disk. Chill for 1 hour.
Preheat the oven to 300°F/150° C. Brush each ring with egg white and dip into sprinkles to coat. Return to baking sheets and bake until golden and puffy, about 15 minutes. Remove from the oven and allow to rest on the pan for 2 to 3 minutes, then transfer to a wire rack to cool. Store in cookie tins.