1. Cream the Butter and Sugars: In a large mixing bowl, using an electric mixer, cream together the softened unsalted butter, granulated sugar, and light brown sugar until the mixture is light and fluffy. This usually takes about 2-3 minutes. The mixture should look pale yellow and airy, not dense.

2. Add Wet Ingredients: Beat in the large egg and vanilla extract until well combined. Scrape down the sides of the bowl to ensure everything is incorporated. Next, add the sourdough discard and mix until just combined. The mixture might look slightly curdled at this point, but don’t worry, it will smooth out.

3. Combine Dry Ingredients: In a separate medium bowl, whisk together the all-purpose flour, baking soda, and salt. Make sure these are thoroughly mixed to ensure even distribution in the dough.

4. Gradually Add Dry to Wet: Slowly add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix; stop as soon as no streaks of flour remain. Overmixing can lead to tough cookies.

5. Fold in Chocolate Chips: Gently fold in the semi-sweet chocolate chips by hand using a spatula. Distribute them evenly throughout the dough.

6. Chill and Prepare for Shaping: Cover the bowl with plastic wrap and chill the dough in the refrigerator for at least 15 minutes. This brief chill helps the dough firm up, making it much easier to roll out and cut. While the dough is chilling, preheat your oven to 375 F (190 C) and line a baking sheet with parchment paper.

7. Roll and Cut Hearts: On a lightly floured surface, roll out the chilled dough to about 1/4-inch thickness. Use a heart-shaped cookie cutter to cut out your cookies. Carefully transfer the cut-out hearts to the prepared baking sheet, leaving about 1-2 inches between each cookie. Re-roll any scraps to cut out more cookies until all dough is used.

8. Bake Until Golden: Bake for 10-12 minutes, or until the edges are lightly golden brown and the centers are just set. The cookies might still look slightly soft in the middle, but they will firm up as they cool. Remove the baking sheet from the oven and let the cookies cool on the sheet for 5 minutes before transferring them to a wire rack to cool completely.