In a small saucepan, add heavy cream and dried verbena leaves over low heat. Here's a picture of the fresh leaves so you know what you're looking for.

If you see them buy them and dry them. It's easy to do and they keep well for tea, desserts, drinks, etc.

You don’t want the cream to simmer, much less boil. Once it’s warm. Turn the heat off and let infuse for an hour or so.

Strain the leaves out. When you’re ready to use it, reheat until it’s just about to simmer. Then in a medium bowl, whisk the sugar, egg yolks and salt. (If you’re concerned about sugar, you can go down a bit on this, but because of the yogurt tang, I wouldn’t go below ¾ cup). Also, if you really like it thick and rich, you could add up to 6 yolks, rather than 4, but it’s not necessary. Once uniform, pour in about half a cup of the hot cream and whisk until smooth. Add in another half cup. Whisk until smooth. Add the rest of the cream. (This process of slowly heating the yolks is called tempering). Add the whole mixture back into the saucepan and cook low to medium low until the custard thickens and coats the back of your spoon.

Return to the bowl, cover, and store in the fridge until completely chilled.

I often do this a day ahead. In a 9x13 pan, whisk the chilled custard and the yogurt. (Sheep’s milk is a high fat yogurt, so if you’re subbing with cow’s milk yogurt, act accordingly- such as considering the additional yolks). Freeze solid. Scrape the frozen ice cream out of the pan. A fork works well. 

Add it to your blender, or even food processor.

Blend until smooth.

Pour into a quart container. Freeze solid. Serve and enjoy the amazing taste of lemon verbena.