These Twix Thumbprint Cookies are deliciously buttery, with a mouthwatering shortbread cookie base. They're little bites of bliss. You might proclaim these cookies even better than Twix candy bars.
In the bowl of a stand mixer, add butter and brown sugar. Using paddle attachment on medium-high speed, mix until fluffy and light, several minutes. Add 3½ cups of the flour and mix on medium-low speed until combined.
On a large board, sprinkle ½ cup flour. Knead dough by hand for 5 minutes, adding as much of the remaining ½ cup flour as needed to make a soft dough. The dough should end up soft and pliable, similar to play-dough, not sticky. (You may not end up using all the flour, depending on how your dough feels.) Divide dough in half, wrap tightly, and chill for at least 30 minutes or until firm enough to roll.
Meanwhile, preheat oven to 325F, with rack on lower middle position. Line baking sheets with parchment paper or silicone mats; set aside.
Working in 2 batches, form dough balls with the chilled dough, about 1-inch each. Form a deep well in the center using the back of a wooden spoon or index finger (you want it deep, but not too wide.) Place 2 inches apart on lined baking sheet and bake 8-10 minutes (these won't brown on top much, but the bottoms should be golden brown.) If needed, very gently depress the centers of baked cookies again. Gently fill centers of cookies with caramel. Let filled cookies cool before drizzling with chocolate.
Place chocolate chips in glass bowl and microwave in 30-second intervals, stirring well in between, just until melted (if it's overdone, it will seize and be unusable.) Transfer melted chocolate to a Ziploc bag, press out air, and seal. Carefully snip a tiny bit off the corner. Use as a pipe to drizzle chocolate over cookies. Let cool and serve.
Notes
We highly recommend making a jar of homemade salted caramel for all your caramel needs (nothing is better than homemade!) However, in a pinch, you can use store-bought salted caramel.