For the cake:
- 1/2 cup dark molasses (not blackstrap)
- 1/2 cup very strong brewed coffee or espresso, cooled to just warm
- 1-1/4 ounces (2-1/2 cups) all-purpose flour; more for the pan
- 2 teaspoons baking powder
- 1/2 teaspoon table salt
- 1/4 teaspoon baking soda
- 1 tablespoon instant espresso powder
- 2 teaspoons ground ginger
- 1/2 teaspoon ground cinnamon
- 1/8 teaspoon ground or freshly grated nutmeg
- 1/8 teaspoon ground cloves
- 10 ounces (1-1/4 cups) unsalted butter, softened at room temperature; more for the pan
- 1-1/4 cups packed light brown sugar
- 3 large eggs plus 2 large egg yolks, at room temperature
For the espresso glaze (optional):
- 1 cup confectioners' sugar
- 1 teaspoon dark rum (optional)
- 1-1/2 tablespoons brewed espresso (or 1-1/2 teaspoons instant espresso powder dissolved in 1-1/2 tablespoons hot water)
Position a rack in the center of the oven and heat the oven to 350ºF. Butter and flour a 10- or 12-cup bundt pan (or four 2-cup mini loaf pans). Tap out any excess flour.
In a liquid measuring cup, whisk the molasses with the brewed coffee. Sift the flour with the baking powder, salt, baking soda, espresso powder, ginger, cinnamon, nutmeg, and cloves.
With a stand mixer (use the paddle attachment) or a hand mixer, cream the butter in a large bowl on medium speed until smooth, about 1 minute. Add the brown sugar and beat until light and fluffy, about 2 minutes. Beat in the eggs and yolks one at a time, stopping to scrape the bowl after each addition. With the mixer on low speed, alternate adding the flour and coffee mixtures, beginning and ending with the flour. Stop the mixer at least one last time to scrape the bowl and then beat at medium speed until the batter is smooth, about 20 seconds.
Spoon the batter into the prepared pan (or pans), spreading it evenly with a rubber spatula. Run a knife through the batter to eliminate any air pockets. Bake until a wooden skewer inserted in the center comes out clean, about 40 minutes (about 30 minutes for mini loaves). Set the pan on a rack to cool for 15 minutes. Invert the cake onto the rack, remove the pan, and let cool until just barely warm. Drizzle with the glaze (if using) and then let cool to room temperature before serving. If you're making the cake ahead, wrap it while still barely warm without the glaze. If you plan to freeze the cake, don't glaze it until you're ready to serve it or give it away.
Combine the confectioners' sugar and rum (if using) in a bowl and, adding the espresso gradually, whisk until smooth. If necessary, add more espresso or water to thin the glaze to a drizzling consistency. When the cake is still barely warm, use a fork or spoon to drizzle the glaze over the top.