Pulse lemon creams in food processor until finely ground.  Add butter and sugar, and pulse until just combined.

Pour crumb mixture into a tart form with a removable bottom.  Press onto the bottom and sides of the form, using a measuring cup to firmly press it down.

Bake in the oven at 350F for 7-8 minutes until done.  If the crust begins to puff up again, gently push it down before allowing to cool and set.

Blend partridgeberries with water (as needed) in a blender or food processor.  Strain over a fine mesh strainer into a bowl - this should be roughly 1 cup of liquid.

Add the sugar and eggs to the bowl and whisk together.   Place the bowl over a pot with 1 inch of simmering water to form a double boiler.  Make sure the bowl does not touch the water.

Whisk continuously until the mixture beings to get thick and many bubbles have formed on the top of the liquid.  Add the butter, one tablespoon at a time to the bowl,whisking until it dissolves before adding the next.

Continue to cook over the double boiler until the mixture has thickened almost to the consistency of pudding.  It will continue to get thick as it cools.

Remove from heat and pour into prepared crust, smoothing the top with a spatula.  Refrigerate until cool.

Whisk the sugar and egg whites in a bowl over a double boiler, until the sugar is dissolved and the egg whites are warm and not gritty when rubbed between two fingers.

In a stand mixer or with an electric mixer, whisk the egg whites until glossy and the meringue holds a peak when the beaters are lifted.

Transfer to a piping bag and pipe small rosettes all around the tart from crust to crust.  Or, simply spoon on the tart and create dips in the meringue with the back of a spoon.

Brown the peaks under an oven broiler or with a kitchen blow torch if you have one.  They can go from golden brown to burnt very quickly, so watch carefully if using the broiler.