Combine chopped plums and 1 ½ cups of sugar in a large pot. Heat the plums over medium-low heat, stirring occasionally. Cook the plums and sugar until the plums release their juices and become very tender. This will take 12 to 15 minutes.

Puree the cooked plum mixture with an immersion blender. Be careful as the mixture is very hot.

Return the pot to the stove and continue to cook at medium to low heat until the mixture thickens and reduces by half. This will take about 10 minutes.

When your jam is finished cooking, you should have approximately 3 ½ cups of plum jam.

At this point, you can test your jam by putting a spoonful on the chilled plate. The jam should be thick and, after two minutes, when you drag your finger through the jam, it should leave a clean separation between the two remaining sections of jam. If it doesn’t, cook your jam for a few more minutes.

In a small bowl, whisk the remaining ⅓ cup granulated sugar with the cornstarch. (This is where I used the lilac infused sugar.) Then, whisk this cornstarch mixture into the jam. Stir occasionally. Cook until the jam reaches a simmer. When it does, simmer for one minute more (be careful at this point not to scorch your jam). Stir in the vanilla extract. Cool the jam until it reaches room temperature.

Heat oven to 350°F.

Line a 9” x 13” baking sheet with parchment paper, overhanging the paper on all the sides.

In a large bowl, combine oats, flour, whole wheat flour, brown sugar, baking powder, salt and cinnamon.

Add the melted butter and mix until the mixture reaches a crumbly consistency.

Press ⅔ of the crumb mixture into an even layer on the parchment-lined baking pan. Spread the jam evenly over the oat mixture. Sprinkle the remaining crumb mixture evenly over the top of the jam.

Bake until the jam bubbles on the edges of the bars and until the oat mixture is a light borwn. This will bake from 45 to 55 minutes. Cool completely before removing from the pan.

Slice the bars into 16 pieces.