Preheat the oven to 325°. Spray a 9 1/2-by-5-inch loaf pan with nonstick cooking spray. In a medium bowl, whisk the cake flour with the lemon zest, baking powder and salt.
In a standing electric mixer fitted with the paddle, beat the butter with the sugar at medium speed until pale and fluffy, about 2 minutes. Scrape down the side of the bowl. Add the eggs one at a time, beating well between additions. At low speed, beat in the flour mixture just until incorporated. Beat in the milk, lemon juice and vanilla, scraping down the side of the bowl as necessary.
Scrape the batter into the prepared pan and bake for about 1 hour and 30 minutes, until the cake is golden and a toothpick inserted in the center comes out clean. Transfer the pan to a rack and let the cake cool for 20 minutes. Unmold the cake and let cool completely, about 3 hours.
Light a grill. Using a serrated knife, cut the pound cake into 10 slices. Lightly oil the grate and grill the slices over moderate heat, turning once, until toasted, about 2 minutes. Transfer to plates. Lightly oil the grate again. Grill the peaches over moderately high heat until lightly browned and tender, about 2 minutes. Spoon the peaches over the cake, dollop with whipped cream and serve.