Step 1

On a lightly floured surface, roll the dough into an 1/8-inch-thick circle. Transfer it to a 9-inch pie plate. Trim the dough to 1/2 inch beyond the plate's rim and flute the edge. Refrigerate for 30 minutes. Preheat the oven to 425°F.

Step 2

Line the crust with a double layer of aluminum foil. Fill with pie weights, dried beans or uncooked rice. Bake the crust on a lower oven rack for 20 to 25 minutes, until the edge is golden brown. Remove the foil and weights. Continue baking for three to six minutes, until the crust bottom is golden brown. Cool completely on a wire rack.

Step 3

In a large, heavy-bottomed saucepan, whisk together the sugar, flour, baking cocoa, salt, water and evaporated milk. Cook, stirring, over medium-high heat for about two minutes, until thickened and bubbly. Reduce the heat to a simmer; cook and stir two minutes longer. Remove from heat.

Step 4

Gradually whisk 1 cup of the hot mixture into the beaten egg yolks. Return the egg yolk mixture to the pan, gently whisking as you pour it in. Bring it just to a gentle boil, stirring constantly. Immediately remove the mixture from heat.

Step 5

Stir the butter and vanilla into the hot mixture. Let it cool slightly. Pour the warm filling into the crust. Let cool for one hour.

Step 6

Chill the pie until set. Serve pie chilled, topped with whipped cream and sprinkled with additional cocoa if desired.