Outrageously Buttery Crumb Cake

INGREDIENTS

• 1 (18.25 ounce) package yellow cake mix
• 2/3 cup water
• 3 eggs
• 1/2 cup butter, softened
• 1 1/3 cups packed brown sugar
• 1 tablespoon ground cinnamon, or to taste
• 1 tablespoon vanilla extract
• 1 1/2 cups butter
• 4 1/2 cups all-purpose flour
• 1 tablespoon confectioners' sugar for dusting (optional)