Have all the ingredients at room temperature. 

Preheat an oven to 350°F. Lightly butter a 10-cup Bundt pan. Dust with flour and tap out the excess. 

In a large bowl, sift together the flour, baking powder and salt. Set aside. 

In the bowl of an electric mixer fitted with the flat beater, beat together the butter and cream cheese on medium-high speed until smooth, about 3 minutes. Reduce the speed to medium, add the sugar and continue beating until light and fluffy, about 2 minutes. 

Beat in the eggs one at a time, beating well after each addition. 

Remove the bowl from the mixer and, using a rubber spatula, fold in the flour mixture until incorporated. 

Stir in the vanilla, lemon zest and lemon juice. Pour the batter into the prepared pan and smooth the top with the spatula. 

Bake until a toothpick inserted into the center of the cake comes out clean, about 1 hour. 

Transfer the pan to a wire rack and let the cake cool in the pan for 30 minutes. 

Meanwhile, make the lemon syrup: In a nonreactive saucepan over medium heat, combine the lemon zest, lemon juice and sugar, stirring until the sugar is dissolved. Bring to a boil, reduce the heat to low and simmer until the syrup is reduced by one-third, 10 to 15 minutes. 

Remove the pan from the heat and let the syrup stand at room temperature until ready to use. 

Tap the sides of the cake pan gently on the countertop to loosen the cake. Invert a flat cake plate or pedestal over the pan and invert the plate and pan together. Tap the bottom of the pan with your hand and lift off the pan. 

While the cake is still warm, poke holes in the surface with a toothpick and brush the cake all over with the lemon syrup, allowing the cake to absorb the syrup before applying more. 

Let the cake cool for 30 minutes more before serving. (The cake can be baked and glazed up to 12 hours in advance. 

Let cool to room temperature, then cover loosely with plastic wrap.) Just before serving, slice the cake into wedges and garnish with lemon slices. Serves 6. 

Source  William-Sonoma