2 sticks (8 oz.) unsalted butter, at room temperature
1 cup sour cream, at room temperature
1 tsp. baking soda
2 cups all-purpose flour
½ tsp. salt
1 ½ cups sugar
1 (7-ounce) tube almond paste, cut into small pieces
4 egg yolks, at room temperature
1 tsp. pure almond extract
Powdered sugar, for serving (optional)
Preheat the oven to 350°F. Butter (or spray with cooking spray) the sides and bottom of a 9-inch springform pan. The line the sides and bottom with parchment paper, and butter (or spray) the paper. In a small bowl, mix together sour cream and baking soda. In another bowl, whisk together the flour and salt.
In the bowl of an electric mixer fitted with the paddle attachment, beat the butter and sugar until fluffy. Add the almond paste a few pieces at a time, and beat on medium speed for 8 minutes. (Yes, this seems like a long time, but do it. The mixture will get gorgeously fluffy.) Beat in the egg yolks one at a time, and mix until incorporated. (If it looks curdled, don’t worry.) Beat in the almond extract and the sour cream mixture. Reduce mixer speed to low, and gradually add the flour mixture, beating just until combined. Using a rubber spatula, fold the batter a couple of times to make sure there’s no unincorporated flour lurking around.
Scrape the batter into the prepared pan, and spread it evenly with the rubber spatula. Bake for about 1 hour: the cake is done when you press the top and it returns to its shape, and also when it shrinks from the sides of the pan. Transfer to a cooling rack, and cool the cake in its pan.
When ready to serve, sift powdered sugar over the top, if you like.