Heat oven to 375°F. Combine graham-cracker crumbs, butter, and 3 tablespoons sugar in a medium bowl; mix well.
Press into a 9-inch pie plate.
Bake until lightly browned, about 12 minutes.
Remove from oven, and transfer to a wire rack until completely cooled.
Lower oven to 325°F. In a medium bowl, gently whisk together condensed milk, egg yolks, and Key lime juice.
Pour into the prepared, cooled crust.
Return pie to oven, and bake until the center is set but still quivers when the pan is nudged, 15 to 17 minutes.
Let cool completely on a wire rack.
Slice and serve with some Homemade Whipped Cream.