How to Make It
Make the cookie shell Preheat the oven to 325°. Line a baking sheet with parchment paper. In a medium bowl, whisk the flour with the espresso powder, baking soda and 1/2 teaspoon of salt. In a stand mixer fitted with the paddle, beat the softened butter with 1/4 cup of the granulated sugar and the brown sugar at medium-high speed until light and fluffy, about 2 minutes. Beat in the egg. At low speed, beat in the dry ingredients until combined.
Scrape the soft dough into the center of the prepared baking sheet. Top with another sheet of parchment paper and roll into a thin sheet. Refrigerate until firm, about 15 minutes. Remove the top paper and bake for about 15 minutes, until golden. Transfer to a rack and let cool completely.
Increase the oven temperature to 350°. Break the cookie into pieces and transfer to a food processor. Add the pecans, the remaining 2 tablespoons of granulated sugar, the orange zest and 1/4 teaspoon of salt and pulse until fine crumbs form. Add the melted butter and pulse to incorporate. Press the crumbs evenly over the bottom and up the side of a 9-inch metal pie plate. Bake for about 20 minutes, until fragrant and browned. Transfer to a rack and let cool completely.
Make the fillings Increase the oven temperature to 400°. Prick the sweet potatoes with a fork, wrap each in foil and transfer to a baking sheet. Roast for about 1 hour, until tender. Let cool slightly.
Split the sweet potatoes lengthwise and scrape the flesh into a medium saucepan. Add the honey and cook over moderate heat, stirring often, until thickened to a paste, about 20 minutes. In a food processor, blend the sweet potatoes with the orange juice until smooth. Spread in the cookie shell and refrigerate until cold, 1 hour.
Meanwhile, in a medium saucepan, bring 2 cups of the milk to a bare simmer over moderate heat. Remove from the heat and add the coffee beans. Let stand for 30 minutes. Strain; discard the coffee beans. In the same pan, bring the coffee milk to a bare simmer over moderate heat.
In a small bowl, whisk the gelatin with the remaining 1/2 cup of milk. In a large heatproof bowl, whisk the granulated sugar with the whole egg, egg yolks, espresso powder and cornstarch. Gradually whisk in half of the hot coffee milk. Scrape the mixture into the same saucepan and bring to a boil over moderate heat, stirring constantly. Cook, whisking constantly, until the pastry cream is thickened, about 2 minutes. Remove the saucepan from the heat and whisk in the gelatin and softened butter.
Scrape the pastry cream into the bowl of a stand mixer. Press plastic wrap directly on the surface and refrigerate until chilled, at least 4 hours.
In the stand mixer fitted with the paddle, beat the pastry cream at medium-high speed until smooth. Switch to the whisk and whip in the heavy cream until fluffy and stiff peaks form, about 1 minute. Mound the pastry cream over the sweet potatoes and smooth the top. Refrigerate until cold, at least 4 hours or overnight. Garnish the pie with candied citrus peel and serve cold.
Excellent small-batch candied citrus peel is available from junetaylorjams.com.