I was first introduced to these delightful gems many years ago in a Paris confiserie. Then a while back I tested a couple of recipes  from my friend Zoë.
It’s been 10 years since I’ve made a batch and I thought it was high time to make them again since the rhubarb in my yard is prolific and now we are in the midst of strawberry season.
8 – 10 stalks red rhubarb, washed and cut into 1-inch pieces
1/4 cup water
3 cups granulated sugar, divided
8 ounces fresh, washed, dried, and hulled strawberries, roughly chopped
Pinch kosher salt
1 teaspoon unsalted butter
2 teaspoons fresh lemon juice
2 pouches (3 oz each) certo liquid pectin
Butter the bottom and sides of an 7 x 7 or 8 x 8-inch pan (depending on how thin you want your final product). Set a piece of parchment paper in the pan allowing it to extend over the sides by a couple of inches. Set a second piece of parchment paper perpindicular to the first; again extending the sides a couple of inches. Butter the bottom and sides of the second piece of parchment with softened butter; set aside.
Place rhubarb in a medium saucepan along with water and ½ cup sugar; bring to a simmer. Cook until rhubarb is completely tender and easily mashed with a wooden spoon. Remove from the heat and allow to cool. Using a blender, purée until smooth. Press puréed rhubarb through a chinois or fine meshed sieve and measure the pulp.
Add ½ cup of rhubarb purée (reserve the remaining) back into the blender along with the chopped strawberries; purée until smooth. Press the puréed mixture through the chinois and measure out 1 1/3 cups. If rhubarb / strawberry purée does not equal 1 1/3 cups add enough reserved rhubarb to equal that amount.
Return the mixture to the saucepan, add 2 cups sugar and lemon juice; bring to a simmer. Insert a candy thermometer into the mixture. When the temperature reaches 140 degrees F stir in butter and skim off any foam that may have accumulated.
Continue cooking until the temperature reaches 238 degrees F. Stir in the pectin and continue cooking for another minute; keeping the temperature from going beyond 238 degrees F.
Remove pan from the heat and using a heat-proof spatula scrape the mixture into the prepared pan. Allow the pâte de fruit mixture to set at room temperature for several hours, until completely cool and firm.
Use a sharp knife to cut into small squares. If serving immediately, toss the individual pieces in remaining ½ cup granulated sugar. Otherwise, store at room temperature and toss in sugar when ready to serve. The candies un-sugared will last at room temperature for about a week.