Clarify the butter, and cool to room temperature. In a mixing bowl combine the eggs, powdered sugar, salt-heavy cream and mix with a paddle attachment until well incorporated. Sift the flour with the baking powder and add with the orange zest, clarified butter and American Pistachios to the mixture above. Mix for three minutes on medium speed. Fill into prepared forms. Bake in a preheated oven at 163°C (325°F). Prepare with the juice of fresh oranges and powdered sugar a very thick paste. Cover the middle part of the cakes with the paste, the thick paste will lightly melt and run over the whole cake. Sprinkle with fine-diced orange peel, or decorate with candied fruits as desired.

Notes:
Clarify - To clear a liquid of all solid particles using a special cooking process. To clarify butter means to melt it and pour off the clear top layer from the milky residue at the bottom of the pan. The resulting clear liquid can be used at a higher cooking temperature and will not go rancid as quickly as unclarified butter.

Clarified butter - Clarified butter is butter, which has been slowly heated up in order to separate the white milk solids (which burn at high heat) from the butterfat. The milk solids (which sink to the bottom of the pan) are discarded and the pure butter fat (clarified butter), which remains are saved for baking. Bakers clarify butter because it has a higher smoking point and they can then bake it without it burning.

Clarified butter need to be at room temperature, so clarify the butter ahead of time. Aluminum foil pans work great for this cake. Use the same oranges for zest and juice. Replace the butter with shortening or lard. Replace the orange zest with lemon or lime zest or a combination of two or all three.

Confectioners' sugar (kuhn-FEHK-shuh-nehrs) - Also called powdered sugar. It is granulated sugar ground to a powder and sifted. Always sift it before using. In Britain it is called icing sugar and in France sucré glace.