Melt the butter in a medium saucepan over medium heat. Stir in the brown sugar and heavy cream; let the mixture come to a boil and boil for 5 minutes without stirring. Remove from heat and stir in a generous pinch of flaky sea salt. Transfer to a jar to cool completely.

(Optional) In a medium saucepan over medium heat, melt the butter. Continue cooking on medium-low, stirring lazily until the butter becomes foamy, then golden, and finally brown with a nutty aroma. Pour into a heat-safe container and cool in the freezer for 10-20 minutes.

In a mixing bowl, add the melted brown butter and whisk in the melted butterscotch chips and sugars. Add the eggs and vanilla, and whisk until smooth. Stir in the dry ingredients until no flour remains.

Cover the dough with a kitchen towel and refrigerate for 10 minutes. Preheat oven to 365?. Line cookie sheets with parchment paper. Scoop dough into 60-gram balls, roll in granulated sugar, and keep extra dough in the fridge.

Place 5-6 dough balls on each cookie sheet and bake for 10 minutes. Cookies will be slightly puffy; gently press down with the back of a measuring cup. Cool on the baking sheet for 5-10 minutes before transferring to a wire rack to cool completely.

In a medium bowl, beat softened butter and cream cheese with an electric mixer until well combined. Gradually beat in powdered sugar, then add butterscotch sauce, vanilla, and a pinch of salt. Mix until smooth; refrigerate if too soft.

Using a small cookie scoop, drop a dollop of frosting on each cookie and spread it with a spatula. Drizzle with butterscotch sauce and add sprinkles if desired.

Enjoy decorated cookies right away or refrigerate for a day before serving. Store leftovers in an airtight container in the fridge for 4-5 days.