Make the Pastry Dough: In a medium size mixing bowl, use a whisk to sift together flour, sugar, and salt. Use a pastry blender to cut the butter and shortening into the dry ingredients until it resembles peas. Whisk together egg and milk in a separate bowl. Add it to the dough, mixing with a large spoon or silicone spatula just until everything comes together.
Divide the dough in half shaping into rectangles, around 3 x 5 inches smoothing the edges. Wrap in plastic wrap, and chill for 30 minutes. (You can also refrigerate the dough for up to 2 days. When doing so, let it rest for 15 to 20 minutes at room temperature before rolling it out.)
Make Strawberry Filling: In a small bowl, whisk cornstarch with cold water just until dissolved. Stir into strawberry preserves, mix well. Set aside. (Chunky fruit preserves or jam works best, not jelly)
Assemble: Place one half of the dough onto a non stick floured surface or silicone pastry mat. Roll into a 12 x 9 inch rectangle about 1/8" thick. Repeat with the second piece of dough. (Keep second half of dough chilled until ready to roll)
Use the edge of a ruler to mark both sheets of dough in thirds lengthwise and widthwise to make nine 3 x 4 inch rectangles. Use a pizza wheel or a sharp knife to cut apart.
Whisk together egg and water. Brush around the edges of each rectangle. Spread about 1 1/2-2 Tbsp of jam down the center of 9 rectangles, leaving about a 1/2-3/4 inch border. Gently lift and place the second rectangle of dough centering it on top. The edges should be even.
Seal the edges of each pop tart using the tines of a fork. Trim any uneven edges. Gently place onto a large parchment lined baking sheet 2 inches apart.
Using the end of a sharp knife, cut 3 even 1/2 inch slits on the top of each pop tart. Place into the fridge and chill on the pan for 30 minutes.
Bake: Preheat oven to 350°F. Remove the pop tarts from the fridge. Bake for 30 to 35 minutes, or just until light golden brown. Remove from the oven, and allow them to cool on the pan for 15 minutes, then carefully remove to a cooling rack to cool completely.
Frosting: Whisk together powdered sugar with almond extract and a pinch of salt. Add 2 Tbsp milk adding more 1 Tbsp at a time just until it's a soft spreadable frosting. Spread on pop tarts, sprinkle with colorful nonpareils or jimmies.
Store in an airtight container at room temperature for up to 3 days or frozen for up to 1 month.