In a small saucepan, combine the candied/dried fruits and/or raisins with the brandy. Heat to warm up everything until the mixture is steamy, then remove the saucepan from the heat and let stand.
Meanwhile, in a medium bowl, whisk together the flour with the spices. Set aside.
In the bowl of an electric mixer fitted with the paddle attachment, cream together the butter and the sugars until light and fluffy. Add the egg and beat well to combine. Scrape down the sides of the bowl as needed.
Add the flour to the mixer bowl in three additions, stirring between each addition and scraping down the bowl as needed. When the last of the flour has almost disappeared into the dough, add the soaked fruit (plus any remaining brandy that didn't get soaked up) and the walnuts. Stir to combine.
Divide the dough into 4 and roll each piece into a log of about 2-inches diameter. Wrap each in plastic wrap and refrigerate overnight.
When you are ready to bake the cookies, preheat the oven at 350ºF (175 °C) . Line a couple half sheet pans with parchment paper.
Slice each log into about ⅛–¼ inch (3–6 mm) thick cookies and arrange on parchment-lined baking sheets spaced 1 inch apart.
Bake the cookies until set, about 12–14 minutes. The longer they stay in the oven, the crisper they will be.
Notes
For the candied fruit, you can use any or even dried fruit, diced fairly fine. Use the same total weight of fruit as in the recipe:
raisins or dried currants
dried cherries or dried cranberries
crystallized ginger
candied citrus peel (lemon, orange, or citron)
glacéed cherries (chop them up in to small pieces!)
dried figs, apricots, or dates
For the nuts, instead of walnuts, you can try toasted almonds, pecans or hazelnuts.
Instead of brandy, you can use spiced or dark rum.
You may want to prepare the candied/dried fruit the day before, soaking it in brandy overnight to give the fruit time to absorb the alcohol and also time to cool down before mixing it into the cookie dough.
Be sure to chill the cookie dough overnight so that it is solid. This way, when you slice and bake the cookies, they will hold their shape quite well.
If any of the cookies break as you slice through the nuts, simply press them back together.