This pastry has at least four different names in Swedish:
Semla, Fettisdagsbulle, Fastlagsbulle or Hetvägg.
Semla derives from the Latin semilia, which was the name used for the finest quality wheat flour or semolina.
Fettisdagsbulle, because it is a bun traditionally eaten today on Fat Tuesday (in other parts of the world known as Mardi Gras, or Shrove Tuesday). Which is TODAY!
Fastlagsbulle, because in Christian liturgical tradition, Fat Tuesday is the last day to go crazy about food before the start of Lent (Sw. fasta or fastlag), i.e. 40 days of fasting and restraint leading up to Easter.
Hetvägg, because someone in history couldn't be bothered to translate German correctly. This name (which in Swedish literally means hot wall, but is derived from German Heisse Wecken meaning hot buns) is mainly used when - according to old traditions - you eat the bun served in a bowl of hot milk. This was traditional dessert on Fat Tuesday. In my childhood, we usually had it every Tuesday throughout Lent (but no other time of the year). We also sprinkled cinnamon on the milk.
Today, the Swedish semla consists of a cardamom-spiced wheat bun which has its top cut off and insides scooped out, and is then filled with a mix of the scooped-out bread crumbs, milk and almond paste, topped with whipped cream. The cut-off top serves as a lid and is dusted with powdered sugar. Nowadays most people have it with coffee or tea - and some cafés have it all year round.
After eating a number of them, though, a period of fasting and restraint is not a bad idea...!
I usually eat just one or two this time of the year, and never felt a craving for one in the summer or autumn!