Step 1Heat the oven to 275 degrees.
Step 2In a large saucepan, combine 3 cups sugar, water and pecans. Bring to a simmer over high heat, then reduce the heat to maintain a gentle simmer, and cook the pecans until softened, about 10 minutes. While the pecans are simmering, combine the cinnamon, ginger, nutmeg and allspice in a small bowl, along with the remaining 1 cup sugar.
Step 3Drain the pecans (discard the pecan simple syrup or save for another use), and place in a large bowl. Sprinkle over the spiced sugar and toss to coat the pecans completely.
Step 4Spread the pecans on a parchment-lined rimmed baking sheet. Toast the pecans until the sugar is hardened and the pecans are dried through, 40 to 60 minutes, tossing every 10 minutes or so.
Step 5Cool the pecans on the baking sheet. The pecans will keep up to 2 weeks stored in an airtight container in a cool place.