Line a baking sheet with parchment paper or a silicone baking mat.
In a heavy-bottomed saucepan, melt butter over medium heat, then add brown sugar and salt.
Whisk vigorously for about a minute, until everything is well-combined and the sugar has melted.
Continue cooking, stirring often, until the mixture reaches right around 300°F on a candy thermometer.Note: if it separates at any point, don't panic. Just remove the pan from the heat and whisk vigorously until it combines again, then return it to the heat and continue cooking.
Once it reaches the desired temperature, immediately pour it onto your prepared baking sheet and let is spread out (you can spread it out further for thinner toffee bits if you want, using a heat-proof spatula).
Let the mixture cool for about 20 minutes, then break it into bits. I found that tapping it with a wooden spoon broke it up nicely, but a knife and cutting board work well too. Or, to avoid flying shards, you can put the toffee into a plastic bag and break it up with a rolling pin or wooden spoon.
Measure out 1 c of toffee bits for your cookies. The remainder can be stored in an airtight container for up to a week. They're great on ice cream, as a cake topping, or just for snacking. ;)
Milk Chocolate Toffee Cookies
Brown HALF of the butter (leave the other half at room temp to soften). See my post on "Brown Butter" for instructions. Pour brown butter into a bowl or other container to cool for 20 minutes.
In a small bowl, combine the flour, salt, and soda. Set aside.
Beat the other half of the butter with the brown sugar until smooth, about 2-3 minutes on medium speed.
Add vanilla, heavy cream, and molasses and mix until combined.
Add the COOLED brown butter and the granulated sugar. Beat until fluffy, about 2 minutes on medium speed.
Add egg and yolk. Beat until well combined, about 1 minute.
Add flour mixture and mix on low just until combined. You should still have some bits of unmixed flour throughout the dough.
Fold in milk chocolate and toffee bits, using a wooden spoon or rubber spatula.
Refrigerate dough overnight (up to 24 hours). This step is CRUCIAL to fully develop the flavors and create the texture we're going for here. You can chill them for a shorter time, but be aware that the cookies will spread more when they bake.When you're ready to bake, set the dough out at room temperature for 10-15 minutes to soften up a bit (it will make scooping a bit easier).
Preheat oven to 350°F. Line 2 cookie sheets with parchment paper or silicone baking sheets.
Using a cookie scoop, ice cream scoop, or your hands, form dough into about 2.5T balls and place 2" apart on a cookie sheet.
Bake for 10-12 minutes, or until beginning to brown around the edges.
Remove from oven and sprinkle with coarse sea salt. Allow the cookies to cool on the cookie sheet for a bit (10ish minutes), then move them to a cooling rack to cool completely.
Store in an airtight container at room temperature for up to 5 days, or freeze for up to a month.