Cut the butter into small pieces, and let sit at room temperature until softened.
In the meantime, lightly grease a 10 inch springform pan with a bit of extra butter, and heat the oven to 350℉.
In a large bowl, beat the eggs and sugar together with an electric mixer on high speed until the mixture is pale yellow, thick, and significantly increased in volume. This will take about 7 to 8 minutes.
Add the softened butter, vanilla extract, almond extract (if using), and salt. Beat the mixture on medium speed until smooth, about 2 minutes.
Add the cranberries (or lingonberries) and the flour. Mix them into the batter by hand with a silicone spatula or spoon. The mixture will be very thick at this point.
Transfer the batter to the prepared pan and spread into an even layer. (If you're using frozen berries, the mixture will be quite stiff, and spreading the batter will feel more like pressing it into the pan.)
Bake for 60 to 70 minutes, or until a tester inserted into the center of the cake comes out clean.
Allow the cake to cool in the pan for 20 minutes. Then prior to unmolding, run a thin knife around the edge of the pan to loosen any sticky areas.
Serve with a dollop of lightly sweetened whipped cream, if desired.