Preheat the Oven:

• Preheat your oven to 350°F (175°C). Grease and flour a 9×13-inch baking pan.

Make the Cake Batter:

• In a large bowl, cream together the softened butter and granulated sugar until light and fluffy.
• Add the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract.
• In another bowl, combine the flour, baking powder, and salt. Gradually add this to the wet ingredients, alternating with the milk, mixing until just combined.

Prepare the Streusel Topping:

• In a separate bowl, mix together the brown sugar, flour, cinnamon, and melted butter until crumbly. Stir in chopped nuts if using.

Assemble and Bake:

• Pour half of the cake batter into the prepared pan, then sprinkle half of the streusel topping over it. Add the remaining batter and top with the rest of the streusel.
• Bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.

Cool and Serve:

• Allow the cake to cool in the pan for about 10 minutes before serving.