Preheat oven to 325°F (170°C). Spray a 9-inch springform pan with baking spray with flour. Line bottom of pan with parchment paper.
In a large bowl, whisk together sugar and melted butter; add eggs, lemon zest and juice, and vanilla bean paste, whisking to combine.
In a medium bowl, whisk together flour, poppy seeds, baking powder, salt, and baking soda. Add flour mixture to sugar mixture, whisking to combine. Whisk in buttermilk just until combined. Pour into prepared pan, smoothing with an offset spatula. Sprinkle evenly with Lemon Poppy Seed Streusel.
Bake until a wooden pick inserted in center comes out with a few moist crumbs, 50 minutes to 1 hour. Let cool in pan for 15 minutes. Remove from pan, and drizzle with Buttermilk Glaze. Serve warm or at room temperature.
Recipe by Bake from Scratch at https://bakefromscratch.com/lemon-poppy-seed-coffee-cake/