In a medium saucepan, toss the strawberries with the caster sugar. Stir to combine and let stand for one hour.
Squeeze the lemon over the strawberry sugar mixture, add it to the saucepan and bring to a simmer over medium-high heat. Skim off any scum that has risen to the surface.
Reduce heat to medium and simmer, stirring occasionally and mashing strawberries, for about 30 minutes or until you’ve reached desired consistency.
Remove from heat and discard the lemon.
Transfer the hot jam to an airtight jar, close the jar and let the jam cool to room temperature. Store in the refrigerator for up to 3 months.
Caster sugar is a superfine sugar that is ground to a consistency between granulated sugar and powdered sugar. Also called baker’s sugar, it works well in this recipe because it dissolves so quickly.