Preliminary: Soak poppy seeds in buttermilk overnight.

Preheat oven to 350 degrees F, 175 degrees C, grease a 10 inch bundt pan. Mix together cinnamon and 1/2 cup sugar. Sprinkle some of the sugar evenly over greased pan to form a thin sugary crust over the cake. Set aside remaining cinnamon sugar mixture.

Cream butter and 1 1/2 cup sugar until light and fluffy. Add eggs one at a time, beating well after each addition. Stir in vanilla.

Sift flour, salt and soda together. Add flour to butter mixture alternating with poppy seed mixture and thoroughly blend.

Pour batter into prepared pan in three goes, sprinkling 1/3 of the remaining cinnamon/sugar mixture between each pouring (you should get three layers if your batter is spread thinly enough).

Bake at 350 degrees F, 175 degrees C, for 50 minutes or until a toothpick inserted in center comes out clean.

Cool cake in pan on wire rack 15 minutes. Turn out onto wire rack and let cool 1 hour.