Position a rack in the middle of the oven and heat the oven to 325°F. Lightly butter and flour a 9-inch-square baking pan.

In a medium bowl, whisk the flour, baking powder, baking soda, nutmeg, and salt until blended.

With an electric mixer, beat the butter, sugar, and vanilla on medium speed until well blended, about 3 minutes. Reduce the speed to medium low and add the eggs one at a time, mixing until just incorporated. Using a wide rubber spatula, alternately fold the flour mixture and the yogurt into the butter mixture, beginning and ending with the flour mixture. Add the chopped cranberries with the last addition of flour.

Scrape the batter into the prepared pan and spread it evenly. Tap the pan gently on the counter to release any air bubbles. Bake for 40 minutes.

While the cake is baking, combine the brown sugar, flour, and cinnamon in a medium bowl. Add the butter and mix, using a fork, until the ingredients are well blended and form small crumbs. Stir in the walnuts and cranberries.

After the cake has Baked for 40 minutes, sprinkle the streusel evenly over the top of the cake. Continue baking until a pick inserted in the center comes out clean, another 10 to 15 minutes.

Cool in the pan on a wire rack until warm or room temperature. Cut into squares and serve.