Prepare a 12-cup tube pan with solid vegetable shortening, then sprinkle with sugar. (If you have a no-fail way of coating your pan so that cakes don't stick, use it. I've found this works best for me.)
Preheat oven to 325 degrees F.
See post above for recommended pans.
In the bowl of an electric mixer, cream butter and shortening together until smooth.
Add sugar and beat until mixture is smooth.
Add eggs, one at a time beat after each addition until yellow disappears into the batter before adding next egg. Stop mixer and scrape sides.
In another bowl, combine gelatin and flour. Whisk to combine.
With the mixer on low, alternatively, add flour mixture and milk beginning and ending with flour. (So you'll add 1/3 flour, 1/2 milk, 1/3 flour, 1/2 milk, 1/3 flour) Stop mixer and scrape sides.
On low, mix in lemon zest and lemon juice.
Spoon batter into prepared pan. Bake at 325 degrees F for 75 to 80 minutes.
Cool in the pan for 15 minutes before inverting onto a serving tray. Serve warm or room temperature. Great served with vanilla ice cream.
Cool completely before covering. Store in an airtight container on the countertop for 4 days or in the refrigerator up to 1 week.