Preheat your oven to 350°F (175°C). Grease and flour a 9-inch cake pan.
In a medium saucepan, combine the chopped prunes and water. Simmer for 10 minutes, then mash lightly and set aside to cool.
In a large mixing bowl, cream together the butter and sugar until light and fluffy. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
In a separate bowl, whisk together the flour, baking soda, cinnamon, nutmeg, and salt.
Gradually add the dry ingredients to the butter mixture, alternating with the buttermilk. Stir in the mashed prunes and pecans (if using).
Pour the batter into the prepared cake pan and bake for 35 minutes, or until a toothpick inserted in the center comes out clean.
While the cake bakes, prepare the glaze. In a small saucepan, melt the butter and brown sugar over medium heat, stirring until smooth. Add the buttermilk and vanilla extract, then bring to a gentle simmer.
Remove the cake from the oven and immediately pour the warm glaze over the top. Let the cake cool in the pan for 10 minutes before transferring it to a wire rack.
Serve warm or at room temperature, allowing the flavors to meld beautifully.
