First, make the bourbon sauce. In a light-colored saucepan, melt the Land O Lakes® Salted Butter over medium-low heat, swirling the pan occasionally, until it starts to foam. Use a heatproof rubber spatula to scrape the bottom and sides of the pan occasionally to prevent the milk solids in the butter from burning. Cook for 5 minutes, or until the butter smells nutty and is amber with dark flecks at the bottom of the pan. Remove from the heat and immediately whisk in the brown sugar and bourbon whiskey. Set on a wire rack to cool while you prep the other ingredients.
Prep your oven and pan. Position a rack in the center of the oven and preheat the oven to 350°F. Spray a 9-inch square cake pan with cooking spray.
Make the pudding. In a large bowl, whisk the eggs until light and foamy. Add the sugar, vanilla, and salt and whisk until combined. Gradually add the milk and whisk until combined.
Place the bread cubes in a large bowl. Pour the pudding mixture over the bread and use a rubber spatula to gently toss the bread until all bread is moistened.
Assemble the bread pudding. Pour ⅓ of the bourbon sauce into the prepared cake pan. Pick up the pan and tilt it from side to side to spread the bourbon sauce across the bottom of the pan. Scoop the bread into the prepared pan and pour any remaining pudding mixture over it. Drizzle another ⅓ of the bourbon sauce over the bread. Use a rubber spatula to press gently on the bread to help it absorb the liquid.
Bake the bread pudding. Bake the pudding for 50 to 55 minutes, or until the sides of the pudding is set but the center still wobbles slightly. A skewer inserted into the center of the pudding should come out with a few crumbs attached.
Serve and store. Serve the bread pudding warm or at room temperature, with a side of the remaining ⅓ bourbon sauce. You can serve it in its baking dish, or pre-slice the pudding into squares for serving. The pudding will keep in an airtight container at room temperature for 1 day. After that, transfer to the refrigerator and refrigerate for up to 2 more days.