Place the buckwheat groats in a skillet set over medium heat. Toast, shuffling the pan frequently, until the buckwheat turns golden and smells nutty, 3-5 minutes. Tip into a medium saucepan to stop the cooking.
Add the milk, vanilla bean and scrapings, sugar, and salt to the pan and heat until steamy and small bubbles appear around the sides of the pan, stirring occasionally to dissolve the sugar and prevent the milk from scorching. Remove from the heat, cover and steep for 20 minutes to infuse with the vanilla and buckwheat.
Pour the heavy cream into a large, heat-proof bowl, place a strainer on top, and set aside. If you have an instant-read thermometer, have it handy.
Place the egg yolks in a medium bowl set on a damp towel to stabilize it. Reheat the milk mixture until hot and steamy. Whisking constantly with one hand, pour the hot dairy very slowly into the yolks. This is called tempering, and prevents the yolks from scrambling. Pour the mixture back into the pot and set the pot over low heat. Cook, stirring constantly with a heatproof silicone spatula, scraping the sides and bottom of the pot, until the custard just begins to “stick” (or form a thickened film) on the bottom of the pot (you may have to tilt the pan to see it), or registers 170ºF (76ºC) on an instant-read thermometer, 5–10 minutes.
Immediately pour the custard through the strainer and into the container of cold cream, discarding the solids. Stir to combine, and chill for at least 4 hours, or preferably overnight. For a quicker chill, pour the ice cream into a metal bowl and place over an ice water bath, stirring until the base is cold.
Place the ice cream base in the freezer for 30 minutes to get it really cold, stirring once or twice (this way the ice cream will take less time to churn, resulting in a denser, creamier ice cream). Pour the mixture into your ice cream maker and process as per the manufacturer’s instructions. Mine takes about 20 minutes to churn.
When the ice cream is finished churning, scrape it into a container. Press a piece of parchment paper directly onto the surface (this will discourage crystals from forming), cover tightly and freeze until firm, at least 2 hours.
Homemade ice cream is best within the first week of being made, but will keep for a month or two in the freezer.