Preheat the oven to 300 degrees. Butter and flour a bundt pan, tapping out excess flour.

In a medium bowl, whisk together the flour, salt and baking soda.

In the bowl of a standing mixer fitted with a paddle attachment, cream the butter and shortening, stopping to scrape down the sides. Slowly drizzle in the sugar; beat the mixture well. Beat in the eggs one at a time, adding the next when the last has been incorporated. Mix in the vanilla. On low speed, mix in a third of the flour mixture until just combined. Add a third of the buttermilk, mixing until just combined. Repeat with the remaining flour and buttermilk. Add the lemon juice, zest, and sesame seeds and mix just enough to combine.

Pour the batter into the prepared pan. Bake until a cake tester inserted comes out clean, about 75 minutes. The top of the cake will be lightly browned, and the sides will shrink slightly from the pan.

While cake is baking, make the simple syrup. Combine the granulated sugar and lemon juice in a small saucepan over medium heat. Stirring constantly, cook until the sugar has dissolved. Remove from heat and set aside.

Invert the slightly cooled bundt cake onto a wire rack set over a large plate or serving dish. Slowly spoon the syrup evenly all over the top of the cake, allowing it to soak in as you go. Allow cake to fully cool before glazing and serving.

Make the glaze: Whisk the confectioners' sugar and lemon juice together in a small bowl. Drizzle over cake. Sprinkle with sesame seeds. Slice and serve.

Make ahead tip: Prepare cake and syrup through step 6. Cover the cake tightly and refrigerate for up to 2 days or freeze up to 2 months. The flavor will be amazing after this time! Bring to room temperature and continue with step 7.