I made a half batch, 6" square pan version of the Mexican Chocolate Brownies Stuffed with Dulce de Leche from The Global Pantry Cookbook. They are very rich and gooey but the flavors are great. Two nice things about the recipe are that the batter gets mixed up in the same pan you use to melt the butter and Mexican chocolate and you line the baking pan with foil so there's no sticky pan to scrub.
I might try a longer bake time in the next round, you can see how gooey they are.
The recipe has you put half the batter in the pan, then drizzle on warmed dulce de leche, then dollop on the remaining batter and gently spread it to cover the dulce de leche. I could work on doing a better job with the spreading as you can see I got some dulce de leche bubbling up around the edges and looking like some sort of fungus:
The photo in the book actually has the same thing going on but since I used Cacao Berry's Extra Brute cocoa powder, my brownies are darker so the dulce de leche stands out more. I need to stash these in the freezer to save myself from them 🙃