1.) To make the cake, position a rack in the center of the oven and preheat to 325 degrees F. Butter and flour a 10-inch fluted tube (Bundt) pan, and tap out the excess flour.
2.) Sift the flour, baking powder, baking soda, and salt together; set aside. Beat the butter and sugar in a large bowl with a hand-held mixer on high speed until light and fluffy, about 3 minutes. Beat in the eggs, one at a time, then the vanilla and zest. On low speed, add the flour in 3 additions, alternating with 2 additions of the sour cream, beginning and ending with the flour, and beat until smooth, scraping down the sides of the bowl often with a rubber spatula. Spread evenly in the pan.
3.) Bake until a wooden skewer inserted in the center of the cake comes out clean, about 1 1/4 hours.
4.) Meanwhile, make the syrup. Bring the lemon juice, zest, and sugar, to a biol over high heat and cook until it is reduced to 1/2 cup, about 15 minutes. Allow syrup to cool before drizzling onto the cake.
5.) Transfer the cake to a wire rack and cool for 10 minutes. Drizzle half of the syrup over the cake. Invert onto the rack and brush with the remaining syrup. Cool completely.