1-First Step: Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper. This prevents sticking and ensures even baking for your double chocolate sandwich cookies.

2-Second Step: In a large bowl, cream 1 cup softened unsalted butter with 1 cup granulated sugar until light and fluffy, about 2-3 minutes. Use a hand mixer for ease. Beat in 2 large eggs one at a time, then add 1 tsp vanilla extract. This builds the wet base.

3-Third Step: In a separate bowl, whisk 2 cups all-purpose flour, 1 cup unsweetened cocoa powder, 1 tsp baking soda, and ½ tsp salt. Gradually mix dry ingredients into the wet mixture on low speed. Avoid overmixing to keep cookies tender. Fold in 1 cup semi-sweet chocolate chips gently.

4-Fourth Step: Scoop tablespoon-sized dough balls onto prepared sheets, spacing 2 inches apart. Flatten slightly with your palm for even sandwiching. Bake 10-12 minutes until edges set but centers look soft. They firm up as they cool, yielding chewy double chocolate cookies.

5-Fifth Step: Cool cookies on sheets for 5 minutes, then transfer to a wire rack. Let them cool completely, about 30 minutes. Warm cookies crumble when filling.

6-Sixth Step: Beat ½ cup softened unsalted butter until creamy. Gradually add 2 cups powdered sugar, ¼ cup cocoa powder, and 1 tsp vanilla extract. Mix in 2-3 tbsp milk until spreadable. Taste and adjust milk for creaminess. For vegan, use plant-based alternatives here.

7-Final Step: Spread 1-2 tsp filling on the flat side of half the cookies. Top with remaining cookies, pressing gently. Yields about 24 chocolate sandwich cookies. Dust with powdered sugar for flair. Store in an airtight container. Gluten-free? Check 1-2 minutes early on bake time. Total time: 45 minutes. Perfect for busy schedules.