Preheat the oven to 350 degrees F (175 degrees C). Cube 1 tablespoon of butter and place in an 8-inch round baking dish.
Place pears in a mixing bowl. Sprinkle with lemon juice and toss to coat. Sprinkle cornstarch over pears and toss to coat. Set aside.
Whisk white rice flour, brown rice flour, buckwheat flour, flaxseed meal, brown sugar, and baking powder together in a mixing bowl. Cut in remaining butter until the mixture resembles coarse pebbles. Add milk, 1 tablespoon at a time, until dough begins to pull together and form a ball.
Pour the pears into the prepared baking dish, covering the cubed butter. Drop walnut-sized balls of dough on top, pushing down to flatten and form a crust.
Bake in the preheated oven until top has browned and pears are bubbling, about 30 minutes. Serve warm.