Using a sharp knife, cut about ¼ inch off top and bottom ends of oranges so fruit can sit flat. Quarter oranges vertically; remove peels, including white pith, in one piece. Cut peel pieces lengthwise into ¼-inch-wide strips. Reserve fruit for another use.
In a large high-sided saucepan, combine peel strips and cold water to cover by 1 inch. Bring to a boil over medium-high heat; drain peel strips. Repeat procedure once.
In a clean large high-sided saucepan, bring sugar and 2 cups (480 grams) water to a boil over medium heat, stirring until sugar dissolves. Add peel strips, arranging in a single layer; simmer, stirring occasionally, until peels are tender and white piths are somewhat translucent, 35 to 40 minutes.
Remove peel strips using a slotted spoon, and arrange in a single layer on a wire rack placed over a parchment paper-lined rimmed baking sheet. Let cool for 1 hour or up to overnight. Reserve syrup for another use.
Recipe by Bake from Scratch at https://staging.bakefromscratch.com/orange-chocolate-brownie-cookies/