Preheat the oven to 180 C or 350 F. Line a 9" x 13" pan with either aluminum foil or baking paper (NOT wax paper). The foil / paper should be large enough to cover the hang from the edges. This will act as handles to take the brownies out later.
In a saucepan set over low heat melt the butter. Once butter is melted, add sugar to combine. Keep heat on low and keep stirring with a whisk every 30 seconds or so till the mixture is hot but not bubbling; it will become shiny looking as you stir it. Heating the mixture to this point will dissolve more of the sugar and produce a shiny top crust on your brownies. Whisking helps in dissolving more sugar.
Once the butter and sugar mixture is at the right temperature turn off heat and then set aside. The mixture should not bubble otherwise it can caramelize or burn.
Meanwhile, crack 4 eggs into a bowl. Add cocoa, salt, baking powder, coffee powder and vanilla. Beat for about 3 - 4 minutes on low speed till mixed together well. Make sure to stop the beater, and scrape the bowl with a spatula to ensure that it is mixed properly.
Add the hot butter/sugar mixture to the egg/cocoa mixture, stirring until smooth. Add the flour, folding it in with a spatula. Once the flour is mixed, add the chocolate chips and fold together.
Spoon the batter into the prepared 9" x 13" pan. Top with spoonfuls dulche de leche and lightly swirl with a knife. Bake the brownies for about 30 – 40 minutes minutes, until a cake tester inserted into the center comes out clean, or with just a few moist crumbs clinging to it.
The brownies should feel set on the edges, and the center should look very moist, but not under-cooked. Additionally, there will be little dots of melted caramel in the brownies.
Remove them from the oven and cool on a rack before cutting and serving.