Preheat oven to 350F and grease a square pan with butter.
In a saucepan, melt the butter and whisk in the cocoa powder, espresso powder, and vanilla extract. Add sugar and let dissolve over low heat.
Remove from heat and whisk in eggs.
Fold in flour and baking powder. Do not over mix! Pour batter into greased pan and top with pretzels. Bake for 30-40 minutes, until baked. Top drizzled with dulce de leche and enjoy!