Preheat oven to 375°F with rack in middle. Generously butter a 9- by 2-inch round cake pan. Line bottom with a round of parchment paper and butter parchment. (SoupAddict's note: I used a 9" springform pan, as I didn't want to disturb the streusel topping when trying to get the thing out of the pan. Feel free to snicker at my chicken heart as you neatly turn your cake out of your regular pan with nary a spilt crumb.)

Scrape seeds from vanilla bean into a food processor with tip of a paring knife (reserve pod for another use if desired). Add sugar and pulse to combine. Transfer to a bowl.

Pulse cranberries with 1/2 cup vanilla sugar in processor until finely chopped (do not purée).

Whisk together 2 cups flour, baking powder, and salt.

Beat together 1 stick butter and 1 cup vanilla sugar in a bowl with an electric mixer at medium-high speed until pale and fluffy. Add eggs 1 at a time, beating well after each addition. Scrape down side and bottom of bowl. Reduce speed to low and mix in flour mixture and milk alternately in batches, beginning and ending with flour, until just combined.

Spread half of batter in pan, then spoon cranberries over it, leaving a 1/2-inch border around edge. Top with remaining batter and smooth top. (SoupAddict's note: the batter is thick and sticky and not very spread-friendly. When you're ready to top the cake with the remaining batter, spoon it in "blops" over the cranberries, covering the layer evenly with as many blops as you can. Then carefully - carefully - smooth the blops over the cranberry layer. Go slowly or you'll end up with cranberries pressed into the bottom layer and scattered throughout the top layer.)

Blend remaining 1/4 cup vanilla sugar with remaining tablespoon each of butter and flour using your fingertips. Crumble over top of cake.

Bake until a wooden pick inserted into cake (not into cranberry fillincomes out clean and side begins to pull away from pan, 45 to 50 minutes. Cool in pan 30 minutes, then remove from pan and cool completely, crumb side up.