Prepare all caramel ingredients, ensuring the heavy cream is at least room temperature to create a smooth, pourable caramel sauce.

Mix water and sugar gently in a heavy-bottomed saucepan, taking care not to let the mixture touch the pot's sides as you blend them.

Heat the saucepan over medium heat, allowing the sugar to dissolve completely without stirring it too much.

Watch the sugar mixture transform – first clear, then light golden, and finally to an amber hue. A gentle nudge might help the sugar along.

Remove from heat immediately when you reach that beautiful amber color, then whisk in the sliced butter until it fully melts.

Pour in the heavy cream slowly while whisking gently, creating a smooth and glossy caramel texture.

Whisk in the vanilla extract and salt, then return the saucepan to medium heat and let it bubble gently for about 2 minutes to thicken slightly.

Stir in the flour until fully combined, then set the caramel aside to cool a bit.

Preheat your oven to 350°F (175°C) and grease a lined 8×8 baking dish with parchment paper for easy removal later.

Whisk together oats, flour, baking powder, and salt in a medium bowl, mixing well before setting aside.

Cream together the softened butter and dark brown sugar in a large bowl until the mixture is smooth and fluffy.

Incorporate the egg, egg yolk, and vanilla into the butter-sugar mix until just combined.

Fold in the dry ingredients, mixing gently until no dry flour is visible. Then, add the semisweet chocolate chips before fully mixing.

Spread about 2/3 of the dough evenly in the bottom of the baking dish, then sprinkle the chopped nuts on top for extra crunch.

Bake for 8 minutes for a deliciously soft base for your bars.

Remove the crust from the oven and immediately top with dark chocolate chips for a melted chocolate surprise.

Pour the cooled salted caramel sauce over the chocolate chips, reheating if it thickened too much to ensure it's pourable.

Dollop the remaining cookie dough on top of the caramel layer, then bake for another 20-25 minutes or until the top turns lightly golden.

Cool the bars at room temperature for about 30 minutes, then pop them in the fridge for 1 hour for easier slicing.

Release the cooled bars from the pan, sprinkle with flaky sea salt, slice, and enjoy the gooey goodness.