Preheat oven to 350 degrees. Lightly grease a tart pan or pie pan with oil or butter.
Heat a small saucepan over medium-low. Add blueberries, sugar, lemon juice, and cornstarch. Simmer gently for 10 minutes until berries break down and become jammy, stirring and smashing the berries with a wooded spoon occasionally. Remove from heat.
In a food processor, chop pretzels until fine crumbs form. Pour into a bowl and stir in butter, brown sugar, and cinnamon. Press into prepared tart or pie pan until evenly distributed. It will rise up the sides of the pan but possibly not the entire way up.
Bake 12 minutes until toasted and firm. Let cool while you prepare the filling.
In a large bowl, whisk the egg yolks until smooth. Add the lemon juice and zest, sweetened condensed milk, vanilla, and salt. Stir until creamy. Carefully pour over the pie crush, scraping any remnants in the bowl with a spatula.
Dollop blueberry jam over the lemon filling. Lightly swirl with a butterknife to create desired pattern.
Bake 15-18 minutes until top is just set. Let cool on a wire rack for 10 minutes, then cover and transfer to the fridge to chill at least an hour. Serve with whipped cream and fresh berries.