Preheat your oven to 180°C (350°F) and grease a 10-inch round baking pan, lining the bottom with parchment paper.
Make the crumble topping
In a medium bowl, mix the flour, brown sugar, cinnamon, and a pinch of kosher salt until well combined.
Pour in the melted butter and stir with a fork or spoon until clumpy crumbs form. Pop the bowl into the fridge to firm up while you make the cake batter.
Make the cake
In a large mixing bowl, combine the cooled melted butter, eggs, granulated sugar, vanilla extract, lemon zest, buttermilk, kosher salt, and Greek yogurt. Whisk vigorously until smooth and completely combined.
Pour the batter into a parchment-lined 10-inch round baking pan and smooth the top with an offset spatula. Scatter the pitted and halved cherries evenly across the top of the batter.
Sprinkle the chilled crumble topping generously over the cherry layer. Gently press down on the streusel with your hands so it adheres to the batter and stays put during the bake.
Bake in a preheated 180°C (350°F) oven for 60–70 minutes. The cake is done when a toothpick inserted into the center comes out clean or with a few moist crumbs.
Let the cake cool in the pan for at least an hour before slicing so it doesn't crumble. Top it with powdered sugar if desired, serve, and enjoy!
Notes
Press the Streusel: Don't skip gently pressing the crumble onto the cake before it goes into the oven. This locks it into the batter so it doesn't spill everywhere when you slice it.
Baking with Frozen Cherries: If you are using frozen cherries, do not thaw them first! Thawing makes them mushy and bleeds excess juice into the cake. Toss them onto the batter straight from the freezer.
Room-Temperature Dairy: Make sure your eggs, yogurt, and buttermilk are at room temperature before whisking. Cold ingredients will seize up the melted butter, resulting in an uneven, lumpy batter.
Don't Overmix: Mix the flour in just until combined. Overmixing develops the gluten, turning a light, tender coffee cake into something dense and bready.
Watch the Toothpick Test: When checking for doneness, try not to poke directly into a juicy cherry, which can make a fully baked cake look wet on the toothpick.