The old English version of Hot Cross buns has a pastry cross instead of a cross made of white frosting. I decided to try these again mainly so I can decorate buns for people who are diabetic or avoiding sugar. Personally my sweet tooth adores a little frosting on my Hot Cross buns, despite the fact its messy and hard to transport, I often carry the buns unfrosted and frost them at my destination.
These are the variations I have found.
Hot cross bun pastry crosses

1. Flour and water
Mixed into a paste and piped on top of the buns before baking.
This doesn't work at all, the paste bakes up hard and inedible.

2. Flour and whole egg

Taken from
https://www.lavenderandlovage.com/2012/03/baking-for-easter-the-history-of traditional-hot-cross-buns-and-hot-cross-bun-recipe.html
1 egg,
1/3 cup sifted white flour
Beat the egg, and mix in the flour to form a soft paste. Place in a plastic bag and pipe on the buns before baking. This makes a soft, bright yellow cross on the bun. The crosses melt down to merge with the bun when baked, unfortunately they also turn brown when baked so not distinct. The cross has about the same texture as the bun not hard or brittle. This makes enough for 15 medium size buns.

3. Jeffrey Hamelman had two hot cross bun cross recipes in his "Bread" book. The original one was flour and water and oil, the second was more elaborate. I modified these heavily so feel free to put them here. His recipes also were for 4 dozen and I only wanted to try a dozen
However the original errata sheet is
http://mellowbakers.com/ErrataSheetFeb2011.pdf

4. Flour and oil and water
4 tbs oil
1/2 cup all purpose flour sifted
1/2 tsp lemon extract
3-4 tablespoons water to make paste
Mix the oil, lemon extract and flour together, Add enough water to form a paste thin enough to pipe from a plastic bag. This was like toothpaste when piped onto the buns before baking. The cross baked up white and crunchy and pretty, like pie crust. However it didn't really merge with the buns and broke off too easily. 3/5/2018

3/12/2018 The second time I tried it, I tried heating the oil and water and then adding the flour. I hoped that sort of cooking would make the pastry easier to handle and less brittle. It was slightly easier to handle like a choux dough, but was still brittle when cooked. It was crunchy like a short pie dough

5. This was sort of based on Jeffrey Hamelman but had no eggs
I tried this on 2/27 and it wasn't bad. I didn't like the sugar in the recipe since I have friends who are avoiding sugar
2 tbs butter
2 tbs sugar
1/4 cup milk +
3/4 tsp vanilla
1/2 tsp lemon extract
7 1/2 tbsp all purpose flour
Melt the butter and sugar together in a pan. Add the milk, vanilla, and lemon extract and stir together. Add the flour. Add enough more milk to get a batter thin enough to pipe through a plastic bag. This was sort of stringy was I mixed it
Pipe this on the buns before cooking. This made a visible paler cross on top of the buns and merged with the buns to be part of them. I didn't really notice any taste or texture, it was like part of the crust

3/12/2018 sugarless variation of the Hamelman inspired cross
3 tbs butter
1/4 cup milk
1/2 tsp vanilla
1/2 tsp lemon extract
1/2 cup flour
Made this like above, heating the butter and milk and then adding flavors, and flour. Added another tablespoon of milk to make soft batter which could be piped. This covered 15 buns and cooked into the crust. This worked out well with a visible light cross on the baked buns.

Outstanding questions, is why do the flour/oil/water versions seem to be seperate from the bun. They just sort of lie on the bun instead of merging. These look like white toothpaste sitting on the buns.
Whereas the flour/butter/milk spreads out and merges with the bun. Its paler but obviously part of the crust and doesn't break off.

Has anyone seen any other variations? I saw one where the cross was more obviously a pie crust and was rolled out and cut into strips and then placed on the bun. I didn't want to do that and stuck with recipes that could be piped out through the corner of a plastic sandwich bag.