strawberry-rhubarb crumble

INGREDIENTS

• 1 1/3 cup flour
• 1 teaspoon baking powder
• 3 tablespoons sugar
• 3 tablespoons Demerara sugar (or turbinado sugar aka Sugar in the Raw)
• Zest of one lemon
• 1/4 pound (1 stick or 4 ounces) unsalted butter, melted
• 1 1/2 cups rhubarb, chopped into 1-inch pieces
• 1 quart strawberries plus a few extras, hulled, quartered
• Juice of one lemon
• 1/2 cup sugar
• 3 to 4 tablespoons cornstarch (some commenters found the flour option a little too, well, floury so this has been updated)
• Pinch of salt