Preheat oven to 350°F. Grease and flour a 9-inch square baking pan, tapping out any excess flour. Set aside.

In a large bowl, whisk together the flour, baking powder, baking soda, poppy seeds, lemon zest and salt. Set aside.

In a separate bowl, cream together the butter and sugar until light and fluffy, about 3 to 4 minutes. Beat in the eggs, one at a time, making sure to mix well after each addition. Stir in the lemon juice and vanilla extract. Reduce the mixer speed to low and add in the flour mixture in two batches, alternating with the sour cream. So half the flour, all of the sour cream and then the remaining flour. Make sure to scrape down the sides and bottom of the bowl as needed. Pour the batter into the prepared baking and spread out into an even layer. Top with the fresh raspberries, slightly pressing each one into the batter.

To make the topping, in a medium bowl, combine the flour, sugar, oats, poppy seeds, nutmeg and salt. Add the butter and rub it in with your fingertips until the mixture resembles coarse crumbs. Sprinkle evenly over the cake batter. Bake, rotating the pan halfway, until a toothpick inserted in the middle comes out clean, about 50 minutes to 1 hour. Transfer to a wire rack and allow to cool completely. Slice and serve with a dusting of powdered sugar if desired. Enjoy!