Place blood orange juice in a small saucepan and bring to a boil, uncovered. Reduce to a high simmer and continue to simmer until the juice has been reduced by about half, 20-25 minutes. Place in fridge to cool.
When brownies are ready to frost, add 1/3 cup of the heavy cream to the cream cheese in a large mixing bowl. Mix on low until completely smooth—you're doing this to eliminate any clumps that might come from the cream cheese. Then add the remaining heavy cream, crème fraîche, honey (adjust sweetness as needed, acidity of citrus may vary), and orange blossom water and mix on high until medium peaks form.
Once the frosting is holding its shape, add in 3 tablespoons of the reduced blood orange juice. Use a silicone spatula to mix.
Once the brownies have chilled in the fridge, slather the frosting on top and sprinkle with finely chopped chocolate to garnish. To slice, run a sharp knife under hot water, dry, and cut. Keep frosted brownies in the fridge until ready to serve.
For a vegan variation, substitute the whipping cream, crème fraîche, and cream cheese for 2-3 cups of chilled coconut cream!