Preheat the oven to 350°F (175°C) and grease a 9-inch round or square cake pan.
In a bowl, whisk flour, baking powder, baking soda, salt, and espresso powder.
In another bowl, beat butter and sugar until creamy. Add eggs and vanilla, mixing well.
Add sour cream to the wet ingredients and mix. Gradually add the dry ingredients, stirring until smooth.
Fold in the mini chocolate chips. Pour the batter into the prepared pan.
In a small bowl, combine brown sugar, flour, butter, and cinnamon to make the streusel.
Sprinkle the streusel over the batter.
Bake for 30-35 minutes or until a toothpick comes out clean.
Let the cake cool on a rack before serving.