Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking pan. Tip: Use parchment paper for easier removal later.

In a large bowl, cream together the butter and sugar until light and fluffy. This should take about 2-3 minutes. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.

Gradually mix in the flour and salt until well combined. Be careful not to overmix to keep the bars tender.

Spread half of the batter into the prepared pan. Sprinkle with half of the pecans and half of the cinnamon. Repeat layers for added flavor.

Using a knife, drag it through the batter to create a marbled effect. This not only looks great but also mixes the flavors nicely.

Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted in the center comes out clean. Tip: Check at the 25-minute mark to avoid overbaking.

Allow the bars to cool in the pan for about 10 minutes before cutting into squares. This helps them set and makes for cleaner cuts.