Blueberry lemon curd: take our already delicious and zingy lemon curd, add blueberries, and you have yourself a shockingly colorful and brilliantly tasty fruit curd that will dazzle your breakfast table.
Add the blueberries. lemon zest and water to a medium (2 quart) heavy-bottomed saucepan set over medium-high heat. Bring to a boil, lower heat and simmer until the blueberries soften and burst, about 5 to 7 minutes. Use a spoon to press berries and break apart berries as they cook.
Strain into a bowl through a fine mesh sieve, pressing pulp with a spoon. Make sure to scrape the puree on the underside of the strainer into the bowl. Allow puree to cool. Discard any unstrained pulp, reserve the puree and rinse the saucepan and sieve.
In a large bowl (or a stand mixer fitted with the paddle attachment), beat the butter and sugar until fully combined, about 2 min. Add the eggs and yolks one at a time, beating each until incorporated. On low, mix in the lemon juice, blueberry puree, salt and cornstarch. The mixture will look curdled, but it will smooth out as it cooks.
Pour the mixture back into the saucepan and cook over low heat until thickened (about 10 to 15 minutes*), stirring constantly. Don’t walk away or you will have lemony scrambled eggs. The curd will begin to thicken at about 170 degrees F, or just below simmer. Once thick, remove from the heat and strain into a bowl through the rinsed sieve. (It will thicken more as it cools).
Add curd to storage jars and allow to cool to room temperature before refrigerating. If using in tarts right away, allow to come to room temperature before filling shells.
Notes
Using a thermometer is a much more helpful than a time estimation since heat can vary. Cook the curd to about 170ºF, though it can go a little higher, if you want it thicker. Just keep stirring and don't let it come to a full boil.