How to Make It
Preheat the oven to 325°. Generously butter a 10-inch Bundt pan and dust with flour. In a medium bowl, whisk the 3 1/2 cups of flour with the salt and baking soda.
In a stand mixer fitted with the paddle, beat the 1 1/2 sticks of butter with the shortening at medium-high speed until smooth. Add the granulated sugar and beat until light and fluffy, about 2 minutes. At medium speed, beat in the eggs 1 at a time until just incorporated, then beat in the vanilla; scrape down the side of the bowl. Beat in the dry ingredients and buttermilk in 3 alternating batches, starting and ending with the dry ingredients. At low speed, beat in the lemon juice.
Scrape the batter into the prepared Bundt pan and use a spatula to smooth the surface. Bake in the middle of the oven for about 1 hour and 15 minutes, rotating the pan halfway through baking, until a toothpick inserted in the center of the cake comes out clean. Let the cake cool on a rack for 30 minutes, then turn it out on a platter or cake stand to cool completely.
In a medium bowl, whisk the confectioners’ sugar with the lemon zest, lemon juice, butter and salt until smooth. Drizzle the glaze over the top of the cake, letting it drip down the sides. Let stand for 20 minutes until the glaze is set. Cut the cake into wedges and serve.