Strawberry Rhubarb Brown Butter Cake

This four-layer strawberry rhubarb cake is one of my favorite cake recipes. The combination of brown butter cake layers with tart strawberry rhubarb compote and lightly sweetened mascarpone is perfectly balanced. I love slicing into this cake to reveal the colorful layers inside.

Although this cake looks impressive, it’s very simple to make. The cake layers come together in just a few minutes, and there’s no fussy steps, like whipping egg whites separately. The strawberry rhubarb filling only requires three ingredients and a little cook time on the stove. And the mascarpone whipped cream is as simple as it gets!

The trickiest part is browning the butter, but it’s really easy when you know what to look for.

Making the brown butter

First things first, you need to make some brown butter. The key to browning butter is letting it cook just long enough before it starts to burn. Follow these steps:

• Slice the butter into a few pieces and melt it in a saucepan over medium-low heat. 
• Continue to cook the butter, watching it carefully. It will sputter and spurt at first, then it will start to quiet down.
• Cook until the bubbles start to subside and the bottom of the liquid begins browning.
• Once the butter takes on a golden brown color, remove it from heat. It should smell nutty and have little brown bits in it. 
• Pour it in a small bowl and let it cool back to room temperature. It should be soft and spreadable when you use it to make the cake batter.

Is my brown butter burnt? 

There are a few ways to tell if you browned your butter too far. These are signs that you burned your butter:

• It smells burnt and/or metallic
• It has little bits of black debris floating in it
• It tastes bitter

If your butter meets that criteria, start over. It will ruin the flavor of your cake.

Perfect browned butter

You will know you’ve browned your butter perfectly if:

• It smells nutty, deliciously toasty, and/or toffee-like
• It’s a caramel color with little brown bits in it
• It tastes pleasant, with a flavor similar to toasted nuts

Strawberry rhubarb cake tips

Once you have perfectly browned butter, the rest of this cake is a snap! While your cakes are baking, make the strawberry rhubarb compote. You can use fresh or frozen fruit for this. If you use frozen fruit, allow it to defrost slightly before you cook it.

Slice the strawberries and cut the rhubarb into small cubes. This will help it to cook and break down faster. Stir the compote often to prevent burning, smashing it with the back of a wooden spoon while it cooks to help it break down. Once the fruit has completely fallen apart and thickened, remove it from the heat. Let the compote cool completely before layering the cake with it.

Then, whip the mascarpone together with sugar, vanilla, and very cold heavy cream. Whisk it just until it forms soft peaks – do not over whip it. You can do this by hand, but a stand mixer or electric beaters will make this a lot easier. Keep the mascarpone whipped cream cold until ready to use.

Assembling and decorating the cake

• Slice each cake in half horizontally to make 4 layers.
• Place the bottom cake layer on a plate and spread strawberry rhubarb compote on top, leaving a little room around the edges.
• Lay the next cake layer on top and spread it with mascarpone whipped cream.
• Add the third cake layer and spread it with more compote.
• Top with the final cake layer.
• Apply a thin layer of mascarpone whip around the entire cake. Chill at least 20 minutes. This is the “crumb coating” and will help seal in the cake crumbs so your final cake is smooth and lovely!
• Finally, frost the cake with the remaining mascarpone whip.

Decorate this strawberry rhubarb cake however you like. Sliced strawberries certainly look beautiful on top! You could also use fresh mint, edible flowers, or freeze-dried strawberries.