Grease the baking pan lightly with butter or oil spray. Dust with flour so the cake releases easily after baking.

Mix brown sugar, flour and cinnamon in a bowl. Add cold butter cubes and crumble with fingers until mixture looks like coarse sand.

In a large bowl, whisk flour, sugar, baking powder and salt. Keep everything evenly combined so the cake texture stays light and tender.

In another bowl, whisk eggs, milk, melted butter and vanilla. Make sure the mixture is smooth and well blended without any streaks.

Pour wet ingredients into dry ingredients slowly. Stir gently until just mixed. Do not overmix or the cake becomes tough and dense.

Pour batter into the prepared pan. Spread it evenly with a spatula. Make sure the corners have batter too.

Sprinkle streusel mix evenly over the top. Cover the whole surface generously because this layer gives sweet crunch and cinnamon aroma.

Place pan into preheated oven at 350°F or 175°C. Bake until golden and a toothpick inserted in center comes out clean and dry.

Let the cake cool in pan for ten minutes first. Then place it on a rack to cool more, so slices hold shape well.

Cut into squares while slightly warm. Serve with coffee, tea or milk. Enjoy the soft cake and crunchy topping together happily.