Position a rack in the center of the oven and heat the oven to 375°F.
Make the topping
In a food processor, combine the flour, sugar, baking powder, and salt. Pulse briefly to blend. Add the cold butter and pulse into 1/2-inch pieces, 5 to 7 pulses. Add the lavender and lemon zest and pulse briefly to combine. Pour the cream over the top and pulse just until moist crumbs form, 8 to 10 pulses.
Turn the mixture out onto a work surface and gently knead until the dough comes together. Lightly flour the dough and roll it into a 9x5-inch rectangle. Cut the rectangle in half lengthwise, and cut each half into four equal pieces. Wrap in plastic and refrigerate.
Make the filling
Tip:Cast iron skillets are great, but not for this cobbler; their reactive surface can lend a metallic taste to the finished cobbler. Stick with a nonreactive skillet, such as stainless steel or enamel-lined cast iron (as shown in the photo).
Put the honey and lavender in a 10-inch nonreactive, ovenproof skillet (8- to 10-cup capacity). Bring to a boil over medium-low heat.
In a large bowl, toss the plums with the cornstarch and salt until evenly coated. Add to the boiling honey mixture and cook, stirring gently, until the plums release some juice and the sauce has thickened, about 6 minutes. Remove from the heat.
Assemble and bake
Spread the fruit into a relatively even layer. Arrange the dough pieces on top of the fruit, leaving spaces between them. Bake until the filling is bubbling and the topping is nicely browned, 30 to 40 minutes. Let sit for about 15 minutes to allow the filling to settle and thicken before serving
Make Ahead Tips
The dough squares for the topping may be made up to 6 hours ahead. Keep refrigerated in plastic wrap until ready to use.
nutrition information (per serving):
Photo: Scott Phillips