How to Make It
Preheat the oven to 350°. Butter and flour a 10-inch springform pan.
In a food processor, pulse the flour with the brown sugar, cinnamon, lemon zest and salt. Add the butter and process until the mixture resembles moist sand. Add the walnuts and pulse 3 times. Transfer the mixture to a bowl and press into large crumbs.
In a medium bowl, whisk the flour with the baking powder, ginger and salt. In a large bowl, using a handheld electric mixer, beat the butter until creamy. Add the sugar and beat until light and fluffy, about 3 minutes. Beat in the honey. Add the lemon zest, vanilla and eggs and beat until smooth. Add the dry ingredients in 2 batches, alternating with the half-and-half and beat at low speed until smooth. Fold in the apples.
Scrape the batter into the prepared pan and smooth the top. Sprinkle with the crumb topping. Bake the buckle in the center of the oven for 1 hour and 15 minutes, or until the topping is golden and a toothpick inserted in the center comes out clean. Let cool for at least 1 hour before unhinging the springform and removing the ring. Cut the buckle into wedges and serve with sweetened sour cream.