Preheat the oven to 365°F (185°C).

In a stand mixer, beat together unsalted butter, dark brown sugar, and granulated sugar on medium-high speed until light and fluffy, about 3-4 minutes.

Add the egg and vanilla extract to the creamed mixture; mix until fully incorporated and smooth, about 1 minute.

Sift together baking powder, baking soda, salt, and all-purpose flour in a separate bowl, then gradually mix into wet ingredients on low speed until just combined.

Gently fold in old-fashioned oats and toffee bits with a spatula until evenly distributed.

Scoop about 3 tablespoons of dough, place a soft caramel in the center, and wrap the dough around it, forming a ball. Repeat and chill in the refrigerator for 2 to 24 hours.

Line baking sheets with parchment paper and place 6-8 cookie balls on each sheet, sprinkling each with a pinch of flaky sea salt.

Bake for 10-12 minutes until edges are golden brown and centers look soft. Reshape slightly if needed after baking.

Let cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.