Prep the oven and pans. Heat oven to 350°F (175°C). Line two baking sheets with parchment paper.
This prevents sticking and keeps cookies soft on the bottom.
Cream butter and sugars. In a large bowl, beat softened butter with brown sugar and granulated sugar until light and fluffy, about 2–3 minutes. This traps air and helps create a tender cookie.
Add eggs and vanilla. Beat in eggs one at a time, then mix in vanilla. Scrape the bowl so everything blends evenly.
Combine dry ingredients. In a separate bowl, whisk flour, baking soda, baking powder, and salt.
Add to the wet ingredients on low speed until just combined. Avoid overmixing to keep cookies soft.
Fold in mix-ins. Stir in mini chocolate chips or your favorite add-ins. Mini chips distribute well and make the edges neater for sandwiches.
Scoop and shape. Use a medium cookie scoop to portion dough onto lined sheets, leaving space to spread.
For uniform sandwiches, weigh scoops or level the scoop each time.
Bake until just set. Bake 8–10 minutes, until edges are set and centers look slightly underbaked. Do not overbake—carryover heat will finish the job, and softness is key.
Cool completely. Let cookies rest on the sheet 5 minutes, then move to a rack. Cool fully so the filling won’t melt on contact.
Make the creamy filling. In a chilled bowl, whip cold heavy cream to soft peaks. Fold in sweetened condensed milk, vanilla, and a pinch of salt.
Adjust sweetness to taste. For chocolate, sift in cocoa powder; for fruity swirls, fold in a ribbon of jam at the end.
Chill the filling briefly. Refrigerate 20–30 minutes to thicken slightly. It should be spreadable, not runny.
If it gets too firm, let it sit at room temp for a few minutes.
Match cookie pairs. Flip half the cookies upside down. Pair similar sizes for even sandwiches.
Assemble. Spread 2–3 tablespoons of filling on the underside of one cookie. Top with its partner and press gently until the filling reaches the edges.
For tidy edges, run an offset spatula around the sides.
Add toppings (optional). Roll the edges in mini chips, sprinkles, or nuts for extra texture and flavor.
Freeze to set. Place sandwiches on a parchment-lined tray and freeze for 1–2 hours, until firm enough to handle and store. This helps them hold their shape.
Store properly. Wrap each sandwich tightly in plastic wrap or place in airtight containers. Label with the date so you remember when you made them.