In a pot, cook blueberries and lemon juice on medium until berries soften. Use the back of a wooden spoon to press the blueberries to release their juices.
Press the blueberry mix through a fine mesh sieve, scraping the bottom of the sieve to get all the juice. You’ll need ¾ cup of juice to make the curd (no more).
Return the blueberry juice to the pot, with the heat off. Once it is cool enough, add the salt, sugar, eggs, yolks, and starch. Whisk to combine.
Turn the heat on and add the butter, whisking frequently as butter melts.
The curd will thicken after about 5 minutes or more, stir it often as it thickens. Let it come to a boil and then sit for about 30 seconds.
Over a bowl place a fine mesh sieve. Pour the curd through the sieve, pressing down to get as much out as possible.
When the crust is golden, remove from oven and pour in the curd. Return to the oven.
Bake for 10-15 minutes until the curd is set.
Let the bars cool at room temperature and then place in the fridge.