1. Step 1: Preheat your oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper, leaving some overhang on the long sides for easy removal.

2. Step 2: Arrange the saltine crackers in a single, tight layer over the bottom of the pan, breaking a few if needed so the entire surface is covered.

3. Step 3: In a heavy-bottomed saucepan, combine the unsalted butter and packed light brown sugar over medium heat, stirring frequently until the butter melts and the sugar begins to dissolve.

4. Step 4: Bring the mixture to a steady boil and cook for 3–4 minutes, stirring occasionally, until it thickens slightly and turns a deeper golden-brown color. Remove from the heat and carefully stir in the vanilla extract and kosher salt.

5. Step 5: Immediately pour the hot toffee mixture evenly over the crackers and gently spread it with a heatproof spatula to cover them completely. Bake for 8–10 minutes, or until the toffee is bubbling all over.

6. Step 6: Remove the pan from the oven and sprinkle the semisweet chocolate chips evenly over the hot toffee. Let them sit for 2–3 minutes, then spread the melted chocolate into a smooth, even layer.

7. Step 7: While the chocolate is still soft, sprinkle the chopped pecans and red and green sprinkles over the top, pressing very gently so they stick into the chocolate.

8. Step 8: Let the toffee cool at room temperature, then refrigerate for 1–2 hours, or until completely firm. Lift the slab out of the pan using the parchment and break or cut it into pieces before serving.