To Macerate the Blood Oranges: thinly slice into thin rounds using a very sharp knife; discard ends and seeds. Place slices into a mason jar, cover with sugar and salt, then seal and shake until well coated. Let sit for 24 hours, shaking occasionally.
To Make the Crust: Preheat the oven to 350°F. In a food processor, add all crust ingredients and pulse together until a dough all comes together and forms 1 ball. Transfer to an 9-inch tart pan with a removable bottom; press the dough firmly with your hands or the bottom of a cup until it covers the entire bottom and up the sides of the pan. To par-bake: place on a sheet pan and bake until lightly golden, 10-15 minutes.
After the blood orange slice have been macerating for 24 hours and a beautiful thick syrup is formed, crack the eggs into a small bowl and give them a quick whisk. Add the eggs to the jar with the blood oranges slices, seal and shake until all is incorporated.
To Assemble the Tart: Place the macerated blood orange slices on the par-baked tart shell and pour the custard over the top. Return to the oven and bake until set, 20-25 minutes. Let cool completely, then slice and serve.