How to Make It
Make the biscotti Preheat the oven to 350°. Line a large baking sheet with parchment paper. In a medium bowl, whisk the 2 1/2 cups of bread flour with the baking soda and salt.
In a stand mixer fitted with the paddle, beat the granulated sugar with the butter and lemon zest at medium speed until pale and creamy, 2 minutes. Beat in the eggs one at a time until incorporated. At low speed, beat in the dry ingredients until the dough just comes together, then beat in the dried cherries.
Scrape the dough onto the prepared baking sheet and, using lightly floured hands, shape it into a 15-by-5-inch log. Bake for about 35 minutes, until golden and just firm, then let cool completely on the baking sheet.
Meanwhile, make the filling In a stand mixer fitted with the paddle, beat the butter with the confectioners’ sugar at medium speed until smooth. Beat in the eggs one at a time until incorporated; scrape down the side and bottom of the bowl as needed. Beat in the almond flour and cornstarch until combined, then beat in the rum. Transfer the almond cream to a medium bowl and refrigerate until just set, about 20 minutes.
Transfer the baked log to a cutting board. Using a serrated knife, cut it crosswise into 1/4-inch-thick slices. Spread a scant tablespoon of the almond cream on half of the slices and arrange them on 2 large parchment paper–lined baking sheets. Spread a teaspoon of cherry jam on the almond cream. Close the sandwiches with the remaining slices.
Bake the biscotti sandwiches for about 15 minutes, until lightly browned and nearly crisp. Let cool completely before serving.