In a medium-sized bowl, whisk together the flour, baking soda, cinnamon, ginger, salt and nutmeg until well blended.
In a large bowl, mix the butter, brown sugar, granulated sugar, egg yolk, pumpkin purée and vanilla until smooth and creamy. Stir in the flour mixture just until combined.
Gently stir in the cornflakes, pecans, pumpkin seeds, almonds, chocolate and cranberries (if using) until combined.
Form the cookie dough into 20 round portions, about 1/4 cup (75g) each. Chill them in the refrigerator for 15-20 minutes. Meanwhile, preheat the oven to 350ºF (180ºC). Line 2 large cookie sheets with parchment paper.
Place the cookie dough balls about 3 inches apart onto the baking sheets. Top each one with a pecan half and a piece of chocolate, if desired. Bake the cookies, one sheet at a time, in the top third of the oven, until the tops are set and the edges are deep golden brown, about 12-14 minutes. The cookies will spread a bit.
Remove the cookies from the oven. Immediately use a large round cookie cutter to shape the hot cookies by sliding it around each one in a circular motion a couple of times, working quickly before they set. Cool the cookies on the cookie sheet for 5 minutes, then transfer them to a cooling rack.