Ingredients
Method
1️⃣ Prep the Pan
Heat your oven to 350°F (175°C). Lightly coat a 9x13-inch baking dish with nonstick spray or line it with parchment for easy removal.
2️⃣ Mix the Dry Ingredients
In a medium bowl, whisk together the flour, baking soda, baking powder, cornstarch, and salt. Set aside.
3️⃣ Cream the Butter & Sugars
In a large bowl, beat the softened butter with both sugars until the mixture looks pale and fluffy. Add the egg and vanilla extract, mixing just until incorporated. Gradually fold in the dry ingredients. Stir gently — don’t overmix. Fold in 1 cup of the white chocolate chips until evenly distributed.
4️⃣ Bake the Base
Spread the thick dough evenly into your prepared pan. Use a spatula (or lightly greased hands) to press it flat. Bake for 12–13 minutes, just until the edges begin turning lightly golden.
5️⃣ Add the Toppings
Remove from the oven and immediately scatter the mini marshmallows and M&M’s over the surface. Return the pan to the oven for 2–3 minutes, just until the marshmallows puff up. Take it out again and sprinkle the remaining ¼ cup white chocolate chips and sprinkles over the warm top.
6️⃣ Cool & Slice
Allow the bars to cool completely before cutting. Slice into squares and store in an airtight container.
Notes
💡 Pro Tips for Perfect Bars
✔ Don’t overbake. The center should look slightly soft when you pull it out. It firms up as it cools. ✔ Press dough evenly. Uneven thickness = uneven baking. ✔ Use room temp butter. Melted butter will change the texture completely. ✔ Line with parchment. Makes lifting and slicing way easier.⚠️ Common Mistakes to Avoid
- Overmixing the dough → leads to dense bars.
- Adding marshmallows too early → they’ll melt flat instead of puffing.
- Cutting while warm → messy, gooey chaos (unless you’re into that).
- Skipping cooling time → structure needs time to set.