Step 1

In a food processor, combine the butter with the sugar, flour, baking soda and salt and process until the mixture forms small crumbs. Transfer to a plate and press into 1/2-inch clumps. Refrigerate for 15 minutes, until firm.

Step 2

In a small saucepan, cook the butter over moderate heat until the solids turn brown, 5 minutes. Immediately scrape the butter and solids into a shallow bowl and freeze until firm but not hard, 15 minutes.

Step 3

Preheat the oven to 350°. Spray a 9-inch springform pan with baking spray and line the bottom with parchment paper. Spray the paper. In a bowl, whisk the flour with the baking powder, baking soda, salt and nutmeg. Scrape the firmed brown butter into the bowl of a standing electric mixer fitted with the paddle. Add the sugar and beat at moderate speed until light and fluffy, 5 minutes. Add the eggs and vanilla and beat until smooth. Working in 3 alternating additions, beat in the dry ingredients and the sour cream, scraping down the bowl occasionally.

Step 4

Scrape the batter into the prepared pan and scatter the crumbs on top. Bake in the center of the oven for 45 minutes, until the cake is golden and a skewer inserted in the center comes out clean. Let cool.

Step 5

Remove the ring and transfer the cake to a plate. Peel the paper off the bottom of the cake before serving.