For the Marzipan

1. Combine all the ingredients in a food processor and pulse for a few seconds until it forms a smooth dough. Shape into a log 2 inches in diameter, wrap tightly and refrigerate. It will keep for up to a month and hardens as it chills, so keep it well wrapped so it doesn’t dry out.

For the Streusel

1. Combine the flour, sugar, baking powder and salt in a medium bowl. Add the cold butter and work it in with your fingers until the mixture forms large, irregular crumbs with some sandy bits.
2. Crumble the marzipan into the streusel and work it in gently with your fingers, until it is evenly worked through. Refrigerate until you’re ready to bake.

For the Crumble

1. Preheat the oven to 375°F. Butter a 9-inch baking dish and set it on a rimmed baking sheet.
2. In a large bowl, toss the cherries with the sugar, tapioca starch, lemon zest and juice and salt until evenly coated. Spread them into the prepared dish in an even layer.
3. Scatter the streusel generously over the cherries and bake for 45-50 minutes if using fresh cherries, 50-55 if using frozen, until the topping is golden and the juices bubble thickly across the center, not just at the edges. If the streusel colors before the fruit is bubbling, tent it loosely with foil.
4. Let the crumble cool for at least 30 minutes before serving. Serve warm or at room temperature with vanilla ice cream or on its own.