In a large saute pan, melt 3 tablespoons of the butter. Add the sugar, 1/2 cup of the brown sugar, lemon juice, and 1 tablespoon flour. Stir the mixture for 1 minute, to dissolve the sugars. Add the rhubarb and cook for 4 to 6 minutes. Add the strawberries and continue to saute for 3 minutes. Add the rum and carefully flame the mixture. Saute for 1 minute. Mix thoroughly and remove from the heat. Cool the filling.
Preheat the oven to 350 degrees F.
In a mixing bowl, combine the remaining 4 tablespoons butter, 1/2 cup brown sugar, 1 cup flour, and sliced almonds. Using your hands, blend well, until the mixture resembles a crumb-like texture.
Pour the rhubarb and strawberry filling into the pie shell. Sprinkle the crumb filling evenly over the fruit filling. Place the pie in the oven and bake until the topping is golden brown and the filling is bubbling. about 45 minutes. Remove the pie from the oven. Let the pie cool on a rack before serving, about 10 minutes. Slice and serve with the vanilla ice cream.
In a mixing bowl combine the flour and salt. Add the lard and work it in with your fingers until the mixture resembles coarse crumbs. Add the water, 1 tablespoon at a time until the dough holds together when pressed. Form the dough a disk and wrap in plastic wrap. Refrigerate for at least 30 minutes.
Roll the chilled disk on a lightly floured work surface into a 12-inch round. Fit it into a 10-inch pie plate, fold and crimp the edges, and refrigerate until ready to fill.