- Fill a pot or other vessel with water. Attach immersion circulator to pot and set temperature to 180℉. Cover and let preheat.
- In a medium saucepan combine half-and-half, vanilla bean seeds, and vanilla pod. Bring to a simmer over medium heat, then take off heat, cover, and allow to infuse for 15 minutes.
- While half-and-half infuses, in a medium bowl whisk to combine egg yolks and agave.
- Remove vanilla bean pod from half-and-half. Return saucepan to medium heat and heat until it just comes to a simmer.
- Slowly whisk half-and-half into egg yolk mixture, whisking constantly as you pour the hot half-and-half in a thin, steady stream.
- Divide custard between 6 small jars (such as jelly jars) with tight-fitting lids. Place lids on top and screw on rings or attach lids. Lower jars into water bath and cook for 45 minutes.
- Remove jars from water bath, let cool on a rack for 30 minutes, then refrigerate to chill completely, at least 3 hours and up to overnight.
- Cut off top and bottom ends of orange, grapefruit, and blood orange so they will sit upright on a cutting board. Use a sharp knife to cut off peel and white pith, following the curve of the fruit to cut off as little flesh as possible. Cut out citrus segments by cutting on either side of the lines of white membrane that run up and down the fruit–you should get beautiful segments with no white pith or membrane. Combine all citrus segments and sliced kumquats in a medium bowl.
- To serve, spoon a little of the citrus compote onto each pot de crème, then sprinkle with pistachios and a pinch of lava salt, if using. Serve immediately.