Preheat your oven to 350°F. Line baking sheets with parchment paper.
In a large mixing bowl, cream together the softened butter, sugar, brown sugar, and ½ cup Biscoff cookie butter until light and fluffy.
Add the egg and beat well. Mix in vanilla.In a separate bowl, whisk together the flour, baking powder, cinnamon, and salt.
Gradually add the dry ingredients to the butter mixture, mixing until just combined.
Using a small cookie scoop or spoon, drop dough balls onto the prepared baking sheet, spacing them about 1-2 inches apart.
Bake for 12-15 minutes, or until the edges are lightly golden.
Melt the remaining ¼ cup of cookie butter for 30 seconds in a microwave. Drizzle over warm cookies and sprinkle with sea salt.
Let cool and dry. Serve.