Make the cake: Preheat the oven to 350℉. Butter and line an 8 or 9-inch baking round with parchment paper.
Place the 4 ounces semisweet chocolate chips and ½ cup unsalted butter in a heatproof bowl set over simmering water, and stir until it melts. Stir in the 1 teaspoon pure vanilla extract. Set aside to cool slightly.
In a large bowl ,whisk together the 1 ¼ cups gluten free flour, 1 cup granulated sugar, 1 ½ teaspoons baking powder, and ½ teaspoon fine sea salt. Whisk or beat in the chocolate mixture, then whisk or beat in the ½ cup whole milk and 2 large eggs until smooth.
Pour the batter into the prepared pan, let it rest for 15-20 minutes, then place it in the oven and bake for about 30-35 minutes. Let cool in the pan set on a wire rack for 10 minutes, then turn it out to cool completely.
Make the frosting: In a large bowl, cream the ½ cup unsalted butter until fluffy, then pour in the ¼ cup salted caramel sauce and beat in the 2-3 cups powdered sugar until incorporated.
Frost the top of the cooled cake with the frosting.
Notes
Can I make it ahead? Yes! If you can, bake the cake the day before you plan to serve it - I always try to bake my cakes a day in advance so that the flavors can fully develop and the crumb firms up, making it easier to frost them. You can frost the cake the day you plan to serve it.
Rest the batter. Build in 20 minutes (or while the oven heats) to rest the batter so that the gluten-free flour can hydrate.
Refrigerate the cake before frosting. Like many gluten free cakes, this one is a tad delicate after it's baked. I like to pop it in the fridge for an hour or up to overnight so that the crumb firms up a bit and doesn't flake off into the frosting. If you do frost the cake at room temperature, make sure to do a thin crumb coat over the top first.
Do I have to use the salted caramel frosting? Absolutely not, although in my opinion, this is one of the best parts of this cake! I've given a few other serving and frosting suggestions in the section below.
Use room temperature ingredients. Bring the butter to room temperature first before you make the frosting. This is essential! A smooth and fluffy frosting with no streaks of cold butter is the vibe we're going for.
Add espresso. Whisk in 1 teaspoon of espresso powder to the dry mix - this will beautifully complement the chocolate flavor without making it taste like coffee!