Combine sugar, water, corn syrup, and salt in a small saucepan over medium-low heat until the sugar dissolves. Increase the heat slightly and cook until the mixture turns a deep golden color and reaches about 340-345°F. Carefully pour in cream (it will bubble), then whisk in butter piece by piece and stir in vanilla. Allow the caramel to cool before using.
Preheat the oven to 350°F (175°C) and grease or line a 9×9-inch pan. Whisk together sugar, flour, cocoa powder, baking powder, and salt in a large bowl. Add melted butter, eggs, and vanilla, mixing until smooth. Fold in milk chocolate chips. Pour into the pan and bake for about 23-25 minutes, checking with a toothpick for moist crumbs.
Let the brownies cool for about 20 minutes. Spread the cooled caramel sauce on top and sprinkle with chopped pecans. For the chocolate drizzle, melt milk chocolate chips with heavy cream, whisk until smooth, and drizzle over the nuts. Finish with a sprinkle of sea salt. Allow toppings to set before slicing.