• Preheat your oven to 350°F/175°C
• Prepare your springform by lining the bottom with baking parchment and greasing the sides with butter.

Brown The Butter

• Get your cake bowl ready and (if you are in a hurry) another, slightly bigger bowl with cold water and ice)
• Before you do anything else, start by browning your butter in a saucepan.
• To do this, melt the butter on medium/high heat until it bubbles, then reduce the heat to medium/low and stir the melted butter until the big bubbles transform in a fine foam.
• This means the water has evaporated and your butter now starts to brown.
• Watch it like a hawk, as it can burn in a heartbeat and keep stirring, so nothing sticks to the bottom of the pot.
• Allow it to cook until it smells nutty and has deeply golden brown specks.
• Take off the heat immediately and pour into your cake bowl, to avoid burning from the remaining heat of the pan.

Method 1: Passive cooling in the fridge (slow)

• Now you can either allow it to cool for about 15-20 minutes in the fridge, until the center of the butter is still liquid, but the outsides are firm.

Method 2: Ice bath (fast)

• Or do what I did and whisk it over an ice bath until solidified but still smooth.
• You’ll have to whisk continuously to incorporate the cold pieces, where the butter is touching your bowl sides back into the warm parts, until you have a really smooth butter.
• Take it out of the ice bath a little before it has reached the perfect creamy texture, as the cold bowl will keep firming it up.
• Why bother with this step? Because melted butter leads to a completely different texture and possibly greasy cake instead of whipping up nicely with the sugar.

Whip The Butter With The Sugar

• Add the sugar to the butter and whip until lighter and fluffy. This is easiest when using a stand mixer. But a whisk and a little workout will do too.

Add Eggs, Liquids and Protein Powder

• Whisk in your eggs until fully incorporated, then the Greek yoghurt, Protein powder (so it can melt into the liquids), vanilla and, if using almond extract.

Fold In Flour And Sourdough Discard

• Mix the baking powder and salt into your flour.
• If you used a mixer, switch over at this point to a spatula.
• Add both flour mix and sourdough discard to the batter and gently fold in until just combined.
• Do not overmix! I did this step in my stand mixer once and it gave me a dense and gummy cake bottom instead of the fluffy and light, buttery sponge we are going for here. And that was just a few seconds of mixing.

Prepare The Plums

• Destone your plums, then slice them, depending on their size.
• Mine where quite large, so I cut them into 6-8 pieces each.

Assemble Your Cake

• Mix the cinnamon sugar.
• Using a large cookie scoop or spoon, cover the bottom of your springform with about half of the batter.
• Lay half of your plum slices over the batter. Try to get this relatively even.
• Sprinkle half of the cinnamon sugar over them.
• Top with the second half of the batter and finish with the second half of the plums. I put them in circles, for decoration, but scattering them over works too.
• Now add the other half of the cinnamon sugar for a pretty and tasty cinnamon-sugar crust.
• This will add sparkly bits, caramelise and give the whole plum cake a lovely warm cinnamon scent with incredible crispy edges.

Bake Your Protein Yoghurt Plum Cake with Sourdough

• Bake for about 45-55 minutes until golden brown and a toothpick inserted into the center comes out clean.
• I always turn my cakes about halfway through baking, to get an even browning, as most ovens I worked with brown slightly unevenly.
• If your cake looks a little too dark before being cooked all the way through, cover with foil for the last 10 minutes. I love mine rather deep golden brown and a little crispy around the edges and didn’t need any foil. But tastes and ovens differ.