Grandmother's Buttermilk Poppy Seed Coffee Cake

Preheat the oven to 350 degrees F (175 degrees C). Grease a 10-inch fluted tube pan (such as Bundt®.

Combine sugar and cinnamon for filling in a small bowl; set aside.

Combine buttermilk and poppy seeds for cake in a small bowl; allow to soak until needed. Sift flour, baking powder, baking soda, and salt together in a medium bowl.

Cream sugar and butter together in a separate bowl. Beat in egg yolks. Add flour mixture in 2 batches, alternating with buttermilk-poppy seed mixture, beating batter briefly after each addition.

Beat egg whites in a glass, metal, or ceramic bowl until foamy. Fold into cake batter with almond extract. Spoon 1/3 of the batter into the prepared pan and sprinkle with 1/2 of the sugar-cinnamon filling; repeat. Spoon remaining batter on top.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 1 hour. Cool in the pan for 1 hour, then loosen cake and invert carefully onto a serving plate.