In a large mixing bowl or stand mixer fitted with the paddle attachment, beat 1 cup softened unsalted butter, 1/2 cup granulated sugar and 3/4 cup packed light brown sugar on medium speed until smooth and pale, about 2–3 minutes. Scrape down the bowl as needed.

Add eggs and vanilla

Add 2 large eggs, one at a time, mixing briefly after each until incorporated. Add 2 teaspoons vanilla extract and mix until combined.

Combine dry ingredients

In a separate bowl, whisk together 2 1/2 cups all-purpose flour, 1 teaspoon baking soda and 1/2 teaspoon salt until evenly blended.

Mix dough

With the mixer on low speed, gradually add the dry ingredients to the butter mixture until just combined. Stir in 1 cup rolled oats, 1 cup semisweet chocolate chips and 1/2 cup toasted chopped walnuts or pecans (if using) by hand with a spatula to distribute evenly; do not overmix.

Portion cookies

Using a 1 1/2 tablespoon cookie scoop (or a tablespoon), drop rounded mounds of dough about 2 inches apart on the prepared baking sheets. Gently press a few extra chocolate chips onto the tops of each dough mound for a finished look. If desired, sprinkle a small pinch of coarse sea salt on each cookie.

Bake

Bake one sheet at a time in the preheated 350°F (175°C) oven for 10–12 minutes, until edges are set and centers are lightly golden but still soft. Rotate the pan halfway through baking for even color.

Cool

Remove from oven and let cookies cool on the baking sheet for 5 minutes to set, then transfer to a wire rack to cool completely. Repeat with remaining dough. Store cookies in an airtight container at room temperature for up to 4 days.

Assorted Truffles

Prepare chocolate

Place 9 oz finely chopped bittersweet chocolate into a heatproof bowl. Have 2 tablespoons each cocoa powder, chopped toasted nuts, shredded coconut and confectioners' sugar placed separately on small plates for rolling.

Heat cream

In a small saucepan over medium heat, warm 1/2 cup heavy cream just until it begins to simmer and small bubbles form around the edge (do not boil). Remove from heat immediately.

Make ganache

Pour the hot cream over the chopped chocolate. Let sit undisturbed for 1 minute to soften the chocolate, then gently whisk from the center outward until smooth and glossy. Add 1 tablespoon unsalted butter and 1/2 teaspoon vanilla extract; whisk until incorporated and smooth.

Chill ganache

Cover the bowl with plastic wrap and refrigerate until the ganache is firm enough to scoop and roll, about 1–1.5 hours. For quicker chilling, spread ganache in a shallow dish and refrigerate 30–40 minutes, stirring occasionally.

Portion truffles

When firm, use a small melon baller or teaspoon to scoop approximately 1 tablespoon portions of ganache. Roll each portion between your palms quickly to form a smooth ball. If the ganache becomes too soft from handling, chill again for 10–15 minutes.

Coat truffles

Roll the truffles in the prepared coatings: cocoa powder, chopped toasted nuts, shredded coconut or confectioners' sugar. For a salted variety, sprinkle a very small pinch of sea salt flakes on several truffles after rolling in cocoa or chocolate. Arrange finished truffles on a parchment-lined tray.

Set and store

Chill the truffles briefly (15–20 minutes) to set the coatings. Store truffles in an airtight container in the refrigerator for up to 2 weeks or at room temperature for up to 48 hours. Bring to room temperature 20–30 minutes before serving for best texture and flavor.

Finishing & Serving

Arrange house-made cookies and assorted truffles on a serving platter lined with parchment paper. Allow cookies to cool fully and truffles to come to room temperature before serving for best taste. Provide small napkins or dessert forks as desired.