Oh yes! It is really about county Småland, or rather: their dialect.
Because of that, The First Thursday in March has become the
National Day of Småland.
In the Småland dialect, the R-sound is inaudible in certain positions.
Ask my wife what comes after thirty-nine, and she will reply Foty
(or rather Fötti).
So, Fössta tosdan i mass is the day when you eat massipantåta.
In normal Swedish Första torsdan i mars and marsipantårta.
The massipantåta in the opening post was presented to me by
one of my clients, on this day, a year ago. Yes, he too came from county
Småland.
Have fun!
Claes in Lund, Sweden