Filling:
16 oz container strawberries, quartered or halved, depending on the size
2 1/2 cups rhubarb, sliced in 1/2 inch slices (about 1 lb)
3/4 cup sugar
1 tbsp lemon zest
1/4 cup cornstarch (I would cut this back to 3 tbsp next time)

Topping:
1 3/4 cups flour
1 tbsp baking powder
1 tbsp sugar
1/4 tsp salt
6 tbsp cold butter, cut into 1/2-inch cubes (3/4 stick)
3/4 cup milk

1 egg

Preheat oven to 375°F.

Combine filling ingredients in a large bowl. Pour into an ungreased 10-inch pie plate or 8x8-inch square baking dish (preferably glass or ceramic - the acidic filling can corrode a metal pan).

Combine flour, baking powder, sugar, and salt in a large bowl or a food processor. Whisk or pulse to combine. Add cubes of butter and cut in with a pastry blender or pulse in food processor until mixture resembles coarse meal. Add milk and mix or pulse until a soft dough forms. Turn out onto a floured work surface and roll or pat to 1/4-inch thickness. Cut into desired shapes and place on the filling.

Alternately, add a little more milk to make a wet dough and drop by spoonfuls on top of the filling.

Brush topping with beaten egg thinned with a tablespoon or two of water. Sprinkle lightly with sugar, then bake until filling is bubbly and topping is golden, about 45-50 minutes. Cover with foil if the topping starts to get too brown before the filling is done.

Cool at least 15 minutes before serving. Serve with whipped cream, if desired.