Combine 3/4 cup of sugar and cream of
tartar in a saucepan. Simmer over low heat, without stirring, until
sugar melts completely and forms a thin brown syrup, 15-20 minutes. When
sugar has completely melted, divide equally between small muffin cups or
flan molds.
Spoon just enough sugar mixture to cover
the bottoms of each container. Let stand until sugar hardens, about 1
minute.
To make the custard mixture, whish the
sugar, egg yolks and eggs. Strain into a bowl. Add the lemon zest and
vanilla essence and blend well. Set aside.
Divide the custard mixture equally between
the muffin cups or flan molds, pouring the custard mixture over the
hardened sugar mixture.
Place the muffin cups or flan molds in a
steamer above a pan of boiling water. Cover with a tight fitting lid and
steam over low heat for 10 minutes, or until firm, making sure the water
does not enter the bolds.
Remove from the heat and set aside to cool
slightly. Run a knife gently around the edges of the molds to loosen the
flans.
Invert onto a serving platter. Serve with
lemon zest and whipped cream, if desired.