Recently, a friend of mine was celebrating a birthday, and although it wasn’t a planned party-type thing, a bunch of friends got together the day after. So of course I asked her if I could make her a cake. I love any excuse to bring a cake to a get together! There’s the obvious reasons. Like, I too would like to eat some cake, and also it’s really fun to get to make a friend a birthday cake. But additionally I love it when I can try new recipes and do a little bit of testing with friends. It means more of my “tests” will get eaten and that means less waste, but I also get their opinions which often help make the recipes that much better.
Over text I asked her what flavors she liked (so I could hopefully make a cake that she would enjoy) and she texted back, “Chocolate!! Coffee, raspberry, pretzels … ? Is this a baking show challenge yet?” 🙂 And so I ended up making my favorite chocolate cake recipe along with a coffee sweetened condensed milk buttercream frosting with salt and raspberries on top. It was a hit!
I wanted to share the sweetened condensed milk buttercream frosting with you all because it was SO yummy and although the version I’m sharing below is flavored with coffee, you could easily change this up for other flavors (see the notes). But one thing I wanted to retest before sharing was I thought the frosting turned out a little bit grainy the night I made that birthday cake. It tasted great, and as it was not just a food experiment but an actual cake I was making for a get together that night, I just had to roll with the less than perfect look. But I wanted to figure out how to perfect that before sharing here.
I am pretty sure my issue was really a couple things. First, I was making this during late July in southern Missouri. It’s very hot and humid, so that can affect butter (and just ingredient temperatures generally) and buttercream frostings are a little temperamental. But also I don’t think I let the coffee cool as much as it needed to. I had much more success when I made the coffee mixture ahead of time and let it completely cool (covered) in the refrigerator so it was the same temperature as the sweetened condensed milk.
If you make this buttercream frosting, you could have a number of minor issues that result in a grainy texture. To fix grainy buttercream, first try mixing on a lower speed for 8-10 minutes. Yes, this is a long time. I have a stand mixer and I left it running for this long on the “2” speed (lower but not the lowest speed). Above, you can see a side-by-side comparison of what the frosting looked like before and after mixing for this long. Mixing it for this amount of time will slightly heat up the butter and help to better mix (emulsify) with the other ingredients. So that plus incorporating a little air as it mixes results in silky smooth, whipped looking buttercream.
If that doesn’t work though, another thing to try is to remove a heaping tablespoon of the frosting and place in a small mug or bowl. Microwave until melted, but not hot. Then with your mixer running on low, drizzle that into the grainy frosting and whip into the silky smooth buttercream consistency you desire.
You may not need these tips though. This sweetened condensed milk buttercream should turn out smooth anyway, but if you have factors working against you (like the coffee mixture may have been too warm, or the humidity is messing with your butter), then try those tips.
This will make a sweet, but not overly sweet coffee buttercream that I love on chocolate cake or brownies. But it would be delicious on vanilla or yellow cake too. It will make enough to frost a standard two-layer cake (basically double what I used on the brownies pictured here).
And if coffee frosting isn’t your thing, you could easily change this up, or try this peanut butter frosting. Happy baking! xo. Emma
Sweetened Condensed Milk Buttercream Frosting
- 2 teaspoons hot water
- 1 packet 3.3 g instant coffee
- 2 cups softened but cold butter
- 1 cup sweetened condensed milk chilled
- 1/2 teaspoon vanilla extract
- 1 1/2 cups powdered sugar
- Combine the hot water and instant coffee until dissolved. Allow to cool. Cover and refrigerate until chilled. Also chill the sweetened condensed milk in the refrigerator.
The butter should be softened but cold. What does this mean? You should be able to dent the butter with your finger easily, but if the butter seems warm or melting at all, then it's softened too much and you should place it back in the refrigerator for a few minutes to firm up.
In a stand mixer, whip the softened, cold butter for a couple minutes. Scrape down the sides of the bowl with a rubber spatula. Then add the sweetened condensed milk and whip until combined. Scrape down the bowl again. Then mix in the coffee mixture and vanilla extract. Last, with the mixer running (or in batches if using a hand mixer), add the powdered sugar in 1/2 cup increments, scraping down the sides of the bowl as needed.
If the frosting appears grainy, check this post for a couple tips to fix this. I used a Starbucks Via Instant packet for the instant coffee here, but other brands/types will work and this may mean the 3.3 grams listed may vary slightly. If you wish to make plain vanilla sweetened condensed milk buttercream frosting, simply omit the hot water and coffee. You could add another 1/2 to 1 teaspoon of another extract to flavor it differently or try mixing in some vanilla beans to enhance the vanilla flavor. Lots of options!