Preheat the oven to 350°F. Butter a 9×13" baking pan.
In a large bowl or mixer, combine flour, oats, graham cracker crumbs, baking powder, salt, brown sugar, and granulated sugar.
Add cold, cubed butter and mix on medium-low speed until the mixture is crumbly and clumps hold together when pressed.
Press half of the crumb mixture firmly into the bottom of your prepared pan. Set the other half aside.
In a mixing bowl, beat the cream cheese until smooth and fluffy.
Add the sour cream and maple syrup or honey, mixing until fully combined.
Beat in egg yolks one at a time, then add lemon zest and vanilla.
Slowly mix in the lemon juice. Add the cornstarch and mix just until incorporated.
Pour the lemon filling evenly over the base.
Warm raspberry jam slightly if thick, then drop small spoonfuls over the filling and swirl gently with a knife or skewer.
Top with remaining crumb mixture, gently pressing it in.
Bake for 30–35 minutes, or until the center is just set and the top is lightly golden.
Cool completely at room temperature, then refrigerate at least 4 hours (preferably overnight) before slicing.