Place cranberries, sugar, and 2 C. water in a saucepan and bring to a boil over medium/high heat. Reduce heat to medium and let simmer for 5 minutes. Add the lemon juice to the pan and bring back to a boil.
Remove from heat and pour through a fine mesh sieve, pressing on the remaining solids to extract excess liquid. Discard solids. Let the cranberry/lemon syrup cool. Stir in the blood orange juice and refrigerate.
To serve: Mix lemonade base with cold water and serve over ice. I like to use a 1:1 ratio of syrup to water, but taste as you add water to find a ratio that you like.
Recipe by The Kitchen McCabe at https://www.thekitchenmccabe.com/2015/02/04/winter-lemonade-cranberry-blood-orange/