A sweet, seasonal treat, semla buns (called fastlagsbulle in Swedish; laskiaispulla in Finnish, or fastelavnsbolle in Danish) are served in Sweden only during Lent.
Emma Bengtsson, the pastry chef at Aquavit in New York City, cuts off the top of these cardamom-flavored wheat buns and removes the filling, replacing it with a creamy almond paste. She then tops the almond cream with whipped cream before making a sandwich with the cut-off top.
In a stand mixer or in a medium bowl, mix the almond paste with the heavy cream until it achieves a smooth, creamy texture. Set it aside in the refrigerator.
In a medium saucepan over medium heat, melt the butter and then add the milk, gently heating the mixture until it becomes lukewarm. Mix the flour, yeast, sugar, egg, salt, and cardamom in the bowl of an electric mixer with the paddle attachment. Stir on medium speed for 10 minutes. Cover the bowl with a damp towel, set it in a warm spot, and let rise for 1 hour.
Punch down the dough, and then using your hands, roll out the buns until they are slightly larger than golf balls. Place them on a greased baking sheet and cover with plastic wrap. Set the tray in a warm place and let the buns rise for 1-2 hours, or until doubled in size.
Preheat the oven to 400 degrees.
Mix the egg yolks with the water and brush the wash on the bun tops. Bake for 15 minutes or until golden.
When cooled, cut a triangle out of the top part of the bun and remove some of the filling. Whip the ½ quart cream until thick, with stiff peaks. Using a spoon or piping bag, fill the cavity with the almond paste. Cover with whipped cream and place the triangle cutouts on top.
Dust with powdered sugar and serve.