In a large pot or pan, combine sugar, orange juice, and 2 cups water over medium heat. Bring mixture to a boil, stirring constantly until sugar has dissolved.
Reduce heat to low and add the orange slices.
Cook orange slices until rind has softened, about 45 minutes, turning them every 15 minutes.
Once softened, transfer slices to a wire rack and cool for one hour.
Blood Orange Curd
In a medium sized heavy-bottomed pot, whisk together sugar and egg yolks until pale and smooth.
Place pan on stove set over medium heat.
Whisk in the blood orange and lemon juice to the egg yolk mixture.
Add the salt and zest.
Cook on medium heat for 4-5 minutes, stirring constantly, or until the mixture coats the back of the spoon.
Once curd has thickened, remove from heat and stir in the butter.
Transfer curd to a bowl, cover, and refrigerate until cold.
Angel Food Cake Roll
Preheat oven to 350 degrees. Line the bottom of a large jelly roll pan (10x15x1") with parchment paper.
In a large bowl, sift ½ cup of sugar and ¾ cup cake flour together.
In the bowl of your mixer add the egg whites, cream of tartar, vanilla, and orange zest; beat on medium speed until soft peaks form.
Gradually add the remaining ½ cup of sugar, about 2 tablespoons at a time, beating on high until stiff peaks form.
Gradually fold in the flour/sugar mixture into the egg whites until combined.
Spoon batter into the parchment lined pan and spread evenly.
Bake for 18-20 minutes, or until the top is golden and the edges begin to shrink away from the pan.
While cake is cooking, spread out a large, clean kitchen towel onto counter. Sprinkle towel with ¼ cup of powdered sugar. Once cake is done baking, loosen edges from pan (if they aren’t already) and flip cake over onto the kitchen towel. Carefully remove the parchment paper then roll the cake up (with the towel inside) beginning with the short end. Allow cake to cool completely- about 1-2 hours.
Once cake has cooled, unroll and spread with curd. Reroll the cake and transfer to a serving dish.
In a clean bowl, beat together heavy whipping cream and powdered sugar until stiff peaks form.
Cover cake with whipped cream and refrigerate until ready to serve. When ready to serve, garnish with blood oranges.