Preheat your oven to 375°F (190°C).

In a mixing bowl, combine the flour and granulated sugar.

Add the chilled butter and cut it into the dry ingredients using your fingers or a pastry cutter until the mixture resembles coarse crumbs.

Mix in the egg yolk and gently knead until a dough forms.

Press the dough evenly into a greased 9-inch pie dish, covering the bottom and sides.

Prick the base with a fork and pre-bake the crust for 15 minutes until lightly golden.

While the crust is baking, prepare the filling. In a bowl, toss the chopped rhubarb with brown sugar and cinnamon. Let it rest for 5–10 minutes.

Spread the rhubarb mixture evenly over the pre-baked crust.

Sprinkle with sliced almonds if desired.

Bake for 25–30 minutes or until the filling is bubbly and the top is golden brown.

Allow the pie to cool slightly before slicing. Serve warm or at room temperature.