This makes a thinner product than the creme fraiche above, but it's technically closer to the traditional Sami method, although reindeer milk is higher in fat (thicker).
Mix the cream and buttermilk or yogurt. Add the chopped angelica to the cream-buttermilk mixture, mix to combine, and transfer to a mason jar or another container with an open top. label, date, and cover the top with cheesecloth.
Place the container in a warm place for 2-3 days, or until it's thickened and tastes strongly of angelica to your liking, remember that as it chills it will thicken even more.
You can also just put the cream and buttermilk in a pan and gently heat it to body temp to speed the process instead of leaving it out, but I'd add the angelica afterwords to keep the aroma.