Preheat Your Oven: Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan or line it with parchment paper.
Cream the Butter and Sugars: In a large mixing bowl, cream together the softened butter, brown sugar, and white sugar until light and fluffy, about 2 minutes.
Add Eggs and Vanilla: Beat in the eggs, one at a time, followed by the vanilla extract, and mix until fully incorporated.
Combine Dry Ingredients: In a separate bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, and salt.
Mix Wet and Dry Ingredients: Gradually add the dry ingredients to the wet ingredients, mixing just until combined.
Add Oats and Raisins: Stir in the old-fashioned oats and raisins (and chopped nuts if using) until evenly distributed.
Bake the Cake: Pour the batter into the prepared cake pan and spread it evenly. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Cool the Cake: Let the cake cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.