Preheat the oven to 375°F and coat a 9x13-inch baking pan with nonstick baking spray. Cream the softened butter with both sugars until light and fluffy, then incorporate the egg, vanilla extract, and creamer (or milk), blending thoroughly. In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt; gradually blend this dry mixture into the creamed base until a soft dough takes shape. Evenly press the dough into the bottom of the prepared pan and bake for 14 to 15 minutes, ensuring not to overbake. Let the bars cool fully before spreading an even layer of salted caramel frosting across the surface. Finish with a sprinkling of coarse sea salt, if preferred. Cut into 24 uniform bars and store in an airtight container to maintain freshness.