Set the oven temperature to 350°F (175°C). Coat a 9 x 13-inch baking dish or a bundt pan with flour and butter.
Mix the all-purpose flour, baking soda, baking powder, and salt in a medium-sized basin. Put aside.
Beat the softened butter and granulated sugar in a sizable mixing basin until the mixture is light and fluffy.
One at a time, add the eggs to the butter-sugar mixture, mixing thoroughly after each addition. Add the vanilla extract and stir.
Add the dry components to the wet ingredients gradually, starting and finishing with the dry ingredients and alternating with sour cream. Blend until barely mixed.
To make the streusel topping, put the ground cinnamon, brown sugar, and chopped nuts in a small bowl.
Evenly spread half of the batter into the pan that has been prepared. Over the batter, scatter half of the streusel mixture.
After adding the remaining batter, level the top. Finally, sprinkle the leftover streusel mixture on top.
To create a marbled look, swish the batter and streusel together with a knife.
Bake for 40 to 45 minutes, or until a toothpick inserted in the center comes out clean, in a preheated oven.
After letting the Christmas Coffee Cake cool in the pan for ten minutes, move it to a wire rack to finish cooling.
If desired, dust with powdered sugar.
Cut into squares and serve, enjoying the festive tastes and delicious texture of the coffee cake. Savor this festive delight while sipping a hot cup of tea or coffee!